• No results found

Original paper A Case Study of a Typical Potato Flavoring based on Aroma Characteristic of Purple Potato

N/A
N/A
Protected

Academic year: 2021

Share "Original paper A Case Study of a Typical Potato Flavoring based on Aroma Characteristic of Purple Potato"

Copied!
12
0
0

Loading.... (view fulltext now)

Full text

(1)

Copyright © 2020, Japanese Society for Food Science and Technology

doi: 10.3136/fstr.26.69 http://www.jsfst.or.jp

Original paper

A Case Study of a Typical Potato Flavoring based on Aroma Characteristic of Purple Potato

Xinzhe G

u1#

, Shengda Y

u1#

, Qiaoyu W

u1

, Shengxiang G

onG1

, Zhengwu W

anG1

, Jinhong W

u1*

and Shaoyun W

anG2

1Department of Food Science and Engineering, Potato Engineering and Technology Research Center, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China

2College of Biological Science and Engineering, Fuzhou University, Fuzhou 350108, China

Received February 26, 2019 ; Accepted August 28, 2019

We investigated the characteristic volatiles of purple potato using sensory evaluation, GC-MS and GC- O, and developed a flavoring formulation based on the information obtained from these tests to apply to potato products. The sensory analysis indicated that roasted and sourish notes gained the highest and lowest scores, respectively, but compositional analysis through GC-MS drew the opposite conclusion, namely that the compounds producing sourish notes accounted for the highest percentage (31.27 %) in all volatiles while roasted notes took up the lowest proportion (5.16 %). GC-O analysis was able to explain this phenomenon, as we identified 2,4-nonadienal, 2,4-decadienal, decanal and 3-octen-2-one as the characteristic volatiles of purple potato. Therefore, the flavor formulation applied to potato products contained higher roasted-note and burnt-note compounds (8.05 % and 6.18 %, respectively) and lower sourish-note compounds (0.05 %), which helped to preserve the original flavors of the purple potato and increase the fine aroma and sweet flavor of potato products.

Keywords: purple potato, aroma characteristic, GC-MS, GC-O, sensory evaluation, flavoring

*To whom correspondence should be addressed.

#: These two authors contributed equally to this paper.

E-mail: wujinhong@sjtu.edu.cn Introduction

Purple potato is a new variety native to Peru in South America. It is rich in nutrients and bioactive components, such as protein, starch, vitamins, minerals, anthocyanins, carotenoids, etc. (Qiu et al., 2018). In particular, purple potatoes have much higher levels of anthocyanins compared to common potatoes. Previous studies indicated that the total anthocyanin content in purple potatoes ranged from 9.5 to 40 mg per 100 g fresh weight (Nemś and Pęksa, 2018). As one class of natural phenolic compounds, anthocyanins possess beneficial properties, such as the ability to scavenge internal free radicals, and prevent hypertension, hyperlipemia and cancer (Kano et al., 2005; Kita et al., 2013; Miyagusuku- Cruzado et al., 2017). Because of this, purple potatoes often contribute to some high-value-added potato products in the

food industry. In addition, the industrialization of potato staple foods has been put forward in China recently. This development strategy plays a vital role in improving the residents’ diet and physique, safeguarding national food security, promoting agricultural structural adjustment, and increasing farmers’ income. For the past few years, researchers have developed Chinese potato products, such as steamed bread, noodles and so on, helping to promote the potato as a staple food (Cao et al., 2019; Zhu et al., 2019). Therefore, the purple potato presents major development opportunities and broad market prospect in the value-added potato product sector.

The aroma property is a vital evaluation index for food quality (Gu et al., 2017; Stafford, 2016), and products with abundant aromas will arouse consumers’ desire to buy and consume. Therefore, it is a worthwhile endeavor to attempt to

(2)

improve the flavor of potato staple food products. Market research indicates that people prefer fine aroma and sweet notes, especially in baked potato products (de Wijk et al., 2018, Zhang et al., 2018). However, it is generally acknowledged that raw and fresh potatoes have weak aromas, which doesn’t arouse the desire to eat these products. It is worth noting that the original and fresh flavor of raw potatoes would easily be weakened or even lost during processing (Zhao et al., 2017), so the application of flavoring can enhance the overall aroma of potato products and increase consumer satisfaction. Therefore, it is very appealing to design a flavoring that would maintain the original aroma profile of purple potato and enhance its sweet note.

Currently, no studies have been done on the aroma of purple potatoes. The volatile compounds of food are often determined by gas chromatography-mass spectrometer (GC- MS) combined with headspace solid-phase microextraction (HS-SPME) (López-López et al., 2018; Niu et al., 2019; Xiao et al., 2017). Compared with some traditional extraction methods (e.g., solvent extraction), SPME has major advantages, including nondestructive detection, simple operation, poison- free treatment and high efficiency (López-López et al., 2018).

Nevertheless, many volatile compounds do not contribute to the aroma profile of a sample because they are not aroma- active compounds and cannot be sensed by the nose (Stafford, 2016). GC-MS cannot be used to distinguish the aroma properties of the volatile compound or determine its contribution to the overall aroma profile of the sample, meaning that key aroma-active volatile compounds cannot be identified using GC-MS. This problem has been resolved by gas chromatography-olfactometry (GC-O). Many studies have confirmed that GC-O is effective in detecting the aroma-active compounds among the volatiles in food, tea, wine, fruit and essential oils (Niu et al., 2019; Xiao et al., 2017; Zhu et al., 2018; Feng et al., 2018). Additionally, GC-O combined with odor activity value (OAV) analysis can determine whether an odorant makes a significant contribution to the characteristic aroma of sample (Xiao et al., 2017; Zhu et al., 2018).

Our work was aimed at determining the characteristic volatiles of purple potato by using GC-MS, GC-O and sensory analysis. We first detected the volatile compounds of samples by GC-MS and determined the characteristic volatiles by combining our GC-MS data with our sensory analysis results.

We then measured the contributions of each odorant to purple potato by GC-O combined with OAV. Finally, we designed a flavor formulation that could be applied to potato products in order to help retain the original flavors of the purple potato, and increase the fine aroma and sweet note of potato products.

Materials and Methods

Materials and chemicals Dried purple potato powder was obtained from Dingxi City, Shaanxi Province, China and bought from a local market in Shanghai in March, 2018. It was

fine-ground before using. All chemicals used in these experiments were of analytical quality and purchased from Sinopharm Chemical Reagent (Shanghai, China).

HS-SPME conditions The SPME fiber (Supelco, Sigma- Aldrich Ltd., USA) was applied to extract headspace volatiles of purple potato powder. It was 1 cm long and coated with divinylbenzene/carboxen/polydimethy-lsiloxane (DVB/CAR/

PDMS, film thickness 50/30 μm). First, the fiber was conditioned at 250 ℃ and aged for 30 min before extraction.

Then 5 g of powder was weighed and transferred into a 50 mL glass vial, where 5 µL of methyl undecanoate (0.171 g dissolved in 36.625 g of ethanol; an internal standard) was added. The glass vial was sealed with tinfoil and heated for 10 min in a water bath at 60 ℃ to equilibrate and gather the headspace volatile compounds. Next, the fiber was inserted into the glass vial at 60 ℃ for 30 min in order to extract volatiles in the sample headspace.

GC-MS GC system (7890A, Agilent Technologies, USA) coupled with a DB-5 capillary column (60 m × 0.25 mm, film thickness 0.25 μm) was employed to separate the volatile compounds found in purple potato powder. After extraction, the fiber was inserted into the GC injection port and thermally desorbed at 250 ℃ for 5 min to ensure that headspace volatile compounds were completely transferred to the GC system. The oven was set to the following program: the initial temperature was held at 50 ℃ for 2 min; then ramped up at 5 ℃/min from 50 ℃ to 150 ℃ and held for 10 min; next, the oven temperature increased to 230 ℃ at a rate of 3 ℃/min and kept at 230 ℃ for 3 min. Helium served as the carrier gas and the flow rate was set as 0.8 mL/min. After the volatile compounds in purple potato powder were separated by GC, they were then identified by the MS system (5975C, Agilent Technologies). The following parameters were used: electron impact mass spectra were recorded at 70 eV; the temperatures of the ion source, quadrupole and transfer line were set as 230 ℃, 150 ℃ and 150 ℃, respectively; and mass spectra were scanned from 50 to 550 amu. Three replicates were run for this experiment.

Identification of volatile components was performed by matching with the standard Wiley (2011) and NIST (2011) library to a similarity value of > 800. Quantitative analysis of identified volatile components was carried out using the method described by Zhang et al. (2019). In consideration of convenience and economy, the relative concentrations of volatiles were calculated according to the added amount of the internal standard (methyl undecanoate) without considering the calibration factors. Calibration factors were considered as 1.00, and the formula was as follows:

Concentration of Analyte = Peak Area of Analyte Peak Area of IS ×

Concentration of IS ···Eq. 1

Where IS was the internal standard.

GC–O Whether the volatile component in samples is sensed by the nose is largely related to the properties of the

(3)

compound. It is worth noting that among a large number of volatile compounds, only a few contribute to the aroma or smell of sample. GC-O can isolate, identify and quantify the aroma-active compounds from sample. In our work, GC-O were performed by an Agilent 7890A GC system combined with an olfactory detection port Gerstel ODP-2. The experimental conditions for the GC-O tests were the same as that of the GC-MS tests. Volatile compounds in the sample were separated by the flow divider valve at the end of chromatographic column before entering a flame ionization detector (FID). Then 50 % of the GC effluent entered the mass detector; the other 50 % was mixed with humidified air and directly entered the sniffing cone.

Five well-trained assessors were selected to perform this experiment. These judges underwent one month of training to ensure that they could confirm the retention time of each aroma-active standard substance and correctly describe its odor quality. Each volatile compound was determined by comparison with the retention time and description of aroma compound. In addition, scores from 1‒5 were used to evaluate the odor intensity of samples in this test, where 1 represented no detection, 2 was slight but detectable aroma intensity, 3 indicated a moderate odor intensity, 4 indicated a relatively stronger intensity, and 5 was for a strong and even sharp intensity. Three replicates were performed for this test.

Odor activity value (OAV) Odor activity value (OAV) is the ratio of the concentration of aroma-active compound to its detection threshold. The thresholds of compounds were from John (2007) and the database by Acree and Arn (2004). The higher the OAV of the component, the greater the contribution to the overall smell of the sample within a certain range. If the OAV is greater than 1, this compound is considered as a key characteristic compound in the overall odor; if it is less than 1, this component has no contribution to the overall odor (Zhang et al., 2019).

Sensory evaluation The sensory evaluation of purple

potato powder was performed by 35 well-trained sensory panelists (17 men and 18 women) between the ages of 25‒35.

Table 1 displays seven appropriate attributes chosen for evaluating aromatic volatiles of purple potato, including earthy, sourish, roasted, burnt, green, fruity and floral. Prior to judging this test, the judges participated in months of training to become familiar with the odors of aroma-active standard substances related to the purple potato. Moreover, a five-class evaluation scheme was carried out in our work, and scores 0‒10 were assigned to every descriptor based on these five classes. The first class indicated the absence of odor (scores 0‒2); the second class represented the presence of slight odor of purple potato powder (scores 2‒4); the third class corresponded to the moderate and clear odor intensity (scores 4‒6); the fourth class expressed a relatively stronger odor intensity (score 6‒8), and the fifth class was for a strong and sharp intensity (score 8‒10) (Beullens et al., 2008).

Preparation of potato flavoring Potato flavoring was prepared based on GC-MS, GC-O and sensory results. Briefly, compounds accompanied with different odor attributes, including earthy, sourish, roasted, burnt, green, fruity and floral, were selected. Then, different amounts of characteristic compounds were applied to the potato flavoring, which was evaluated by the sensory analysis. Then, the optimal proportion of ingredients was determined through the comparison of sensory scores. Finally, non-flavored and flavored purple potato powder were evaluated by GC-MS and sensory analysis.

Data analysis In this work, data is displayed in the form of mean values ± standard deviation. One-way ANOVA followed by Duncan’s test ( p < 0.05) was carried out to measure the significance of our data.

Results and Discussion

Sensory analysis The aromatic characteristics of purple potato were determined by 35 experienced analysts. As shown in Table 1, seven attributes (earthy, sourish, roasted, burnt, Table 1. Descriptors for purple potato powder in the sensory evaluation.

Odor descriptors Descriptions Representative aromatic compounds earthy earthy odor, pungent aroma generated by

fermented starch 1-octen-3-ol, 1-pentanol

sourish relatively higher threshold straight chain acid containing less than 6 carbon, such as acetic acid and hexanoic acid

roasted sweet and ripe flavor generated by hot

processing; low threshold 3-methional burnt burnt odor, accompanied with powder

incense from cereal starch 2,5-dimethylpyrazine, 2-pentyl furan

green smell from fresh grass hexanal, 2-nonenal

fruity sweet aroma from ripe fruit some compounds containing 8‒10 carbon, such as nonanal

floral sweet aroma from flowers, accompanied

with aromas of nuts and fermentation benzaldehyde, isovaleraldehyde

(4)

green, fruity, and floral) were employed to describe the aroma of samples via sensory analysis. As seen in Fig. 1, purple potato powder presented the highest roasted and earthy notes, earning scores of 7‒8, followed by burnt, fruity and floral notes with scores of 6‒7, whereas sourish and green notes remained at lower levels (scores of 3‒5). These scores were statistically different with different letters ( p < 0.05). The roasted note was significantly different from others in the sensory score, but earthy, burnt and fruity notes had no significant differences with each other. The result demonstrated that roasted, earthy, burnt, fruity and floral notes from the samples showed relatively stronger odor intensity, whereas sourish and green notes displayed moderate odor intensity. No attributes expressed a slight or sharp aroma intensity. In our work, roasted and burnt notes appeared as a sweet and ripe flavor, meanwhile floral and fruity notes gave people a pleasant and satisfied sense (de Wijk et al., 2018). Earthy and green notes corresponded to unripe and groundy smell of raw potato, which brought unpleasant feelings to people (Filly et al., 2015).

Identification of volatile compounds by HS-SPME-GC-MS Firstly, we detected the volatiles in purple potato powder at different temperatures (25, 40, 60, 80 ℃) by HS-SPME-GC- MS. Our results (Supplementary Table 1) showed that samples generated more characteristic volatiles at higher temperatures (60 ℃ and 80 ℃) compared with lower temperatures (25 ℃ and 40 ℃). This is perhaps because heating helps accelerate the volatilization of aroma-producing compounds in purple potato powder. Therefore, higher temperature conditions were beneficial to enrich the characteristic volatiles of purple potatoes. However, high temperatures strengthen interactions

between components, which could cause significant changes in the qualities of components and alter the original odor retention (Gu et al., 2017; Sun et al., 2010). The effect of temperature on the odor of purple potato powder was analyzed by GC-MS to determine the contribution of the seven attributes discussed above, including earthy, sourish, roasted, burnt, green, fruity and floral notes. (Supplementary Fig. 1). Results showed that the proportion of green and sourish notes, the representative aromas derived from raw and fresh purple potato (Song and Liu, 2018; John, 2007), decreased at higher temperatures. On the contrary, roasted and burnt notes increased under high temperatures, which mainly came from the thermal interactions between components. Therefore, volatiles generated by samples at 60 ℃ contained more sourish and green notes than 80 ℃, making 60 ℃ be the idea temperature for the enrichment of volatile compounds of purple potato powder.

A total of 27 characteristic volatile compounds were detected from the solid-phase microextraction of purple potato powder by GC-MS at 60 ℃, as listed in Table 2. These substances belonged to olefin, alcohol, ketone, aldehyde, acid, aromatic and nitrogenous compound groups. Of the identified compounds, hexanoic acid was the most highly concentrated, with a value of 8.63 µg/g, followed by 5-pentyl-2(5H)-furanone (4.60 µg/g) and 3,5-octadiene-2-one (2.55 µg/g). Previous studies have indicated that hexanoic acid produces a fatty and cheesy odor and is representative of sourish notes (Xia, 2008;

John, 2007). As shown in Fig. 2, volatile compounds producing sourish attributes accounted for the highest proportion (31.27 %) of characteristic volatiles, followed by green, earthy and fruity attributes. This result is consistent with previous Fig. 1. Sensory scores of seven descriptors for evaluating aromatic volatiles of purple potato.

Different letters (a‒e) indicate significant differences ( p < 0.05) in the sensory scores of seven descriptors of purple potato.

(5)

Table 2. Aroma-active volatiles detected in purple potato powder at 60 ℃ by HS-SPME- GC-MS.

No. RIa Rtb Compounds Content

(µg/g) Identification

1 668 7.14 Propanoic acid 0.20 ± 0.00 MS, RI, Rt

2 741 8.71 1-Pentanol 0.13 ± 0.05 MS, RI, Rt

3 801 9.66 Hexanal 1.17 ± 0.19 MS, RI, Rt

4 828 10.22 Methyl pyrazine 0.10 ± 0.03 MS, RI, Rt

5 844 11.24 2-Hexenal 0.10 ± 0.02 MS, RI, Rt

6 911 12.24 Pentanoic acid 0.43 ± 0.05 MS, RI, Rt 7 910 13.12 2,4-Hexadienal 0.17 ± 0.05 MS, RI, Rt 8 892 14.55 2,5-Dimethyl pyrazine 0.23 ± 0.04 MS, RI, Rt

9 957 14.61 2-Heptenal 0.20 ± 0.08 MS, RI, Rt

10 960 14.96 Benzaldehyde 0.90 ± 0.10 MS, RI, Rt

11 982 15.37 1-Octen-3-ol 0.23 ± 0.05 MS, RI, Rt

12 993 15.71 2-Pentyl-furan 0.83 ± 0.21 MS, RI, Rt 13 1 019 16.57 Hexanoic acid 8.63 ± 0.26 MS, RI, Rt 14 1 033 17.22 dl-Limonene 0.53 ± 0.34 MS, RI, Rt 15 1 040 17.32 3-Octen-2-one 1.73 ± 0.54 MS, RI, Rt 16 1 049 17.66 Benzeneacetaldehyde 0.17 ± 0.05 MS, RI, Rt

17 921 17.97 2-Octenal 0.40 ± 0.08 MS, RI, Rt

18 1 095 18.33 3,5-Octadiene-2-one 2.55 ± 1.05 MS, RI, Rt 19 1 047 21.28 2-Ethenyl-6-methyl pyrazine 0.63 ± 0.24 MS, RI, Rt

20 1 209 22.54 Decanal 0.80 ± 0.22 MS, RI, Rt

21 1 217 22.94 2,4-Nonadienal 1.03 ± 0.17 MS, RI, Rt 22 1 283 25.10 Cinnamaldehyde 0.27 ± 0.05 MS, RI, Rt 23 - 25.44 Nonanoic acid, ethyl ester 0.17 ± 0.05 MS, Rt 24 1 324 26.57 Decanoic acid, methyl ester 0.65 ± 0.05 MS, RI, Rt 25 1 317 26.63 2,4-Decadienal 0.43 ± 0.24 MS, RI, Rt 26 - 27.81 5-Pentyl-2(5H)-furanone 4.60 ± 1.15 MS, Rt

27 1 147 30.86 2-Nonenal 0.10 ± 0.02 MS, RI, Rt

a: retention index, b: retention time

Volatiles were identified by comparison of retention index, retention time and MS spectra with the standard Wiley (2011) and NIST (2011) libraries.

Fig. 2. The percentage of the volatile compounds belonging to different descriptors in total volatiles of purple potato at 60 ℃ by GC-MS.

(6)

reports that green, sourish and earthy notes were characteristic volatiles of raw and fresh potato (Song and Liu, 2018). Green notes, with hexanal (1.17 µg/g) and 2-nonenal (0.10 µg/g) as representative compounds, occupied the second highest proportion (18.72 %), while fruity notes, produced by compounds containing 8‒10 carbons, made up 12.26 % of total characteristic volatiles. And fruity notes brought up fresh and gentle feelings in people, contributing to the pleasantness of the purple potato aroma (Gu et al., 2017; Sun et al., 2010; Song and Liu, 2018). Roasted notes were mainly generated by heterocyclic compounds, such as methyl pyrazine (0.10 µg/g) and 2-ethenyl-6-methyl pyrazine (0.63 µg/g), and accounted for the lowest percentage (5.16 %) of all the characteristic volatiles. Burnt notes, generated by 2,5-dimethylpyrazine, 2-pentyl furan, and other similar compounds, occupied 8.85 % of the volatiles. These aroma-active compounds were generally accompanied with powder incense from cereal starch.

Interestingly, the GC-MS results were contrary to the sensory results, where sourish and green notes were at lower levels in the sensory evaluation test. This discrepancy mainly resulted from the odor threshold of volatile compounds (Li et al., 2019;

Zhu et al., 2018). For example, roasted notes were at a lower concentration in the volatiles of samples, but the compounds producing these notes had a low detection threshold. Thus, it is possible that roasted notes contributed significantly to the overall flavor of purple potato, despite being present at a relatively low concentration.

Identification of characteristic aroma compounds by GC-O combined with OAV Twenty-seven compounds were detected when characteristic volatiles of the purple potato were screened by GC-MS. However, the concentration of the aroma-active

compound is not the only factor that determines whether a particular compound plays an important role in the aroma profile of a sample. Importantly, the odor threshold also had significant influence on the sensory detection of each volatile compound. Therefore, the odor activity value (OAV) of an aroma-active compound, as determined by the concentration and odor threshold, was analyzed combined with GC-O and used to evaluate the results.

Values of strength of odor intensity of identified volatile compounds of purple potato varied from 1 (not detected), 2 (weak), 3 (medium), 4 (strong), 5 (extremely strong). And thirteen main aroma-active compounds, with odor intensity greater than 2, were detected by GC-O in the samples at 60 ℃.

These compounds included aldehyde, olefine, ketone, ester, alcohol and aromatic compound (Table 3). The odor attributes of these compounds ranged from earthy, fatty, spicy, and green, to fruity and floral as well. As shown in Table 3, 1-octen-3-ol, 3-octen-2-one, 2,4-nonadienal, and 2,4-decadienal displayed strong odor intensity, with a score greater than 4. These compounds contributed to the aroma profile of purple potato powder, and played a vital role in the sensory analysis.

Additionally, hexanal, 2-hexenal, 2-pentyl-furan, dl-limonene, decanal, cinnamaldehyde decanoic acid, and methyl ester provided odor intensity ranging from 3 to 4. These compounds were mainly linked to green, vegetable, earthy, citrus and fatty attributes. These descriptors are more easily identified as green and earthy notes, and acted as important modifiers in the aroma of the purple potato.

The OAVs of 13 aroma-active compounds are displayed in Table 3, which suggests that 4 odorants (OAV > 1) are the characteristic aroma-active volatiles of the purple potato Table 3. Identification of characteristic compounds by GC-O and OAV.

No. RIa Rtb Compounds Description Threshold

(µg/g) Content

(µg/g) OAV Strength

1 801 9.66 Hexanal fatty-green 4.5 1.17 ± 0.19 0.26 ± 0.05 3.33 ± 0.72

2 844 11.24 2-Hexenal leaf-green 17 0.10 ± 0.02 0.01 ± 0.00 3.00 ± 0.65

3 910 13.12 2,4-Hexadienal fatty, green 10 0.17 ± 0.05 0.02 ± 0.01 2.67 ± 0.49

4 957 14.61 2-Heptenal vegetable 13 0.20 ± 0.08 0.02 ± 0.01 2.67 ± 0.49

5 982 15.37 1-Octen-3-ol earthy 1 0.23 ± 0.05 0.23 ± 0.06 4.33 ± 0.49

6 993 15.71 2-Pentyl-furan earthy, vegetable 6 0.83 ± 0.21 0.14 ± 0.04 4.00 ± 0.65

7 1 033 17.22 dl-Limonene fruity 10 0.53 ± 0.34 0.05 ± 0.04 3.33 ± 0.49

8 1 040 17.32 3-Octen-2-one earthy 1 1.73 ± 0.54 1.73 ± 0.67 4.67 ± 0.53

9 1 209 22.54 Decanal sweety, citrus 0.3 0.80 ± 0.22 2.67 ± 0.88 3.67 ± 0.72 10 1 217 22.94 2,4-Nonadienal fatty, chicken 0.09 1.03 ± 0.17 11.48 ± 2.31 5.00 ± 0.00

11 1 283 25.10 Cinnamaldehyde spicy 50 0.27 ± 0.05 0.01 ± 0.00 3.33 ± 0.49

12 1 324 26.57 Decanoic acid, methyl ester fatty, cognac 4.3 0.65 ± 0.05 0.15 ± 0.02 3.33 ± 0.49 13 1 317 26.63 2,4-Decadienal fatty, citrus 0.1 0.43 ± 0.24 4.33 ± 2.89 4.67 ± 0.49 a, retention index; b, retention time

Thresholds of compounds were from the literature by John (2007) and the database by Acree and Arn (2004).

(7)

powder. 2,4-nonadienal had the highest OAV of 11.48, followed by 2,4-decadienal (4.33), decanal (2.67), and 3-octen- 2-one (1.73). Among these compounds, 2,4-nonadienal produced a fatty and chicken-like odor, which was the representative aromatic compound for roasted or burnt notes, and produced the characteristic aroma of baked potato products. This compound caused roasted notes to obtain the highest score in the sensory evaluation test. In the same way, 3-octen-2-one, 1-octen-3-ol and 2-pentyl-furan mainly volatilized different earthy notes, and their relatively lower thresholds led to the second highest sensory scores for earthy notes. In addition, decanal and 2,4-decadienal produced sweet and citrusy scents, which were often identified as fruity or floral notes.

On the other hand, hexanoic acid generated sourish notes, and it had both the high concentration (8.63 µg/g) and detection threshold (3 000 µg/g), leading sourish notes to score the lowest in the sensory analysis. Similarly, hexanal contributed a relatively higher amount (1.17 µg/g) to the volatile mixture, but it had a relatively lower OAV (0.26) and did not contribute much to the aroma profile of purple potato powder. These results are in agreement with the sensory analysis, which found that green notes were present at a low level in the total odor.

Determination and evaluation of the flavoring formulation equipped with the aromas from purple potato Based on our sensory analysis results, we concluded that the aroma-active compounds producing roasted, burnt and earthy notes contributed more to the characteristic aroma of purple potato.

GC-MS analysis indicated that the compounds producing sourish notes accounted for the highest percentage of volatiles, followed by green, earthy and fruity notes. GC-O results, however, showed that the aroma-active compounds giving off roasted or burnt notes made higher contributions to the aroma profile of purple potato powder. As mentioned above, roasted and burnt notes were characteristic of baked potato products;

fruity and floral notes were representative of the sweet aroma from ripe fruits; green, earthy and sourish notes were typical of raw and fresh potato. We must consider the total aroma of purple potato and people's preference for sweet flavors when designing the flavoring formulation. In general, roasted, burnt, fruity and floral notes would provide fine aroma and sweet flavors, while earthy, green and sourish notes gave people feelings of soil, unripe fruits and fermentation. Therefore, we designed the flavoring formulation to contain compounds accompanied with different floral, roasted and burnt notes (namely 10, 7, and 12 compounds, respectively). These compounds helped to increase the fine aroma and sweet flavors normally produced by the purple potato. A few sour-aroma (3 compounds) and green-aroma compounds (2 compounds) were also included in the flavoring formulation, in order to add the characteristic flavor of raw and fresh potato (Table 4).

Compounds producing roasted, burnt and floral scents made up 8.05 %, 6.18 %, and 1.31 % of all ingredients, respectively,

Table 4. Recipe of potato flavoring.

Compounds Content (%)

Sourish note

Acetic acid 0.01

Butyric acid 0.02

Propionic acid 0.02

Floral note

Benzaldehyde 0.06

Phenethyl alcohol 0.005

Geranium oil 0.002

Benzyl alcohol 0.8

Isovaleraldehyde 0.001

2-Methylbutyraldehyde 0.002

d-Limonene 0.004

dl-Citronellol 0.03

beta-Damascone 0.4

Ethyl acetate 0.006

Roasted note

Dimethyl sulfide 0.04

Methional/3-(Methylthio)propionaldehyde 0.4 5-Hydroxyethyl-4-methylthiazol 5

Dimethyl disulfide 0.01

Furfuryl alcohol 0.2

Furfural 0.1

Furaneol 2.3

Green note

Hexanal 0.02

2,4-Decadienal 0.005

Burnt note

Acetyl-2-pyrazine 0.2

2-Acetylfuran 0.3

Cyclotene 0.01

2-Ethyl-3,(5 or 6)-dimethylpyrazine 0.03

2-Acetylpyrrole 0.02

2,3-Dimethylpyrazine 0.25

2,5-Dimethylpyrazine 0.08

2,3,5-Trimethylpyrazine 0.15

2-Methylpyrazine 0.06

3,4-Dimethyl-1,2-cyclopentadione 0.02

2-Ethylpyrazine 0.06

Maltol 5

Lactonic-sweety note

delta-Decalactone 0.1

delta-Dodecalactone 0.3

Vanillin 9.5

Solvent

Propylene glycol 74.485

Total 100

(8)

while lactonic and sweet compounds comprised 9.9 %.

Compounds giving off sourish and green aromas were added at a much lower percentage, at 0.05 % and 0.025 % of the mixture, respectively. The solvent, in this case propylene glycol, occupied the remaining 74.485 % in the flavoring formulation.

Finally, Fig. 3 (A and B) shows the total icon chromatogram

(TIC) of non-flavored and flavored purple potato powder by GC-MS. After adding flavoring, the amounts of volatiles increased and odor intensity of purple potato powder was enhanced. This indicated that the flavoring could enhance the breadth and intensity of the aroma profile of purple potato products. The results of our sensory evaluation tests, as detailed in Fig. 4, demonstrated that the odor intensity of almost all Fig. 3. Total icon chromatogram of non-flavor added (A) and flavor added purple potato powder (B) by GC-MS at 60 ℃.

Fig. 4. Sensory scores of non-flavored and flavored purple potato powder.

(9)

attributes, except earthy and sourish notes, slightly increased after adding the flavoring. Roasted notes presented a particularly strong odor intensity, earning scores greater than 8.

Roasted, burnt, floral and fruity notes appeared as sweet and ripe flavors, and gave a pleasant and satisfied sense to people.

Earthy and sourish notes, on the other hand, corresponded to thoughts of soil, unripe fruits and fermentation, which might not be favored by consumers. In consideration of the further consumer evaluations, the flavoring is added into purple potato products in order to reduce the proportion of the earthy and sourish notes and increase others, which helps to potently improve consumers' preference and increase product acceptability.

Conclusion

This study identified the characteristic volatiles of purple potato by GC-MS, GC-O and sensory analysis, and designed a flavoring formulation that could be applied to potato products.

Based on the sensory analysis, roasted, earthy, fruity, burnt, floral notes were stronger, while green and sourish notes were present at lower levels. GC-MS results, however, indicated the compounds accompanied by sourish notes accounted for the highest percentage (31.27 %) of the volatiles, followed by green (18.72 %), earthy (15.24 %) and, fruity compounds (12.26 %), whereas floral, roasted and burnt notes comprised a lower proportion of the mixture at 8.50 %, 5.16 % and 8.85 %, respectively. The discrepancy can be explained by our GC-O results showing that the overall aroma profile depended on both the concentration and odor threshold of the aroma-active compound. Furthermore, GC-MS and GC-O analysis identified 2,4-nonadienal, 2,4-decadienal, decanal, and 3-octen-2-one as the characteristic volatiles of purple potato, and confirmed their strong odor intensity in the overall smell. Hexanoic acid, which produces sourish notes, did not dominate the aroma of purple potato despite being present in much higher amounts than the other volatiles because it had a higher odor threshold.

Therefore, the flavoring formulation contained 8.05 % roasted note compounds, 6.18 % burnt note compounds, 1.31 % floral note compounds, 0.05 % sourish note compounds, 0.025 % green note compounds, and 9.9 % lactonic or sweet compounds. This formulation helped to increase the fine aroma and sweet flavor of potato products. In addition, the flavoring contributed to enhanced odor intensity of the entire aroma and increased the number of volatiles of purple potato powder, which can increase the quality of potato products.

Acknowledgments The research was financially supported by the National Key R&D Program of China (Grant No:

2016YFD0400206) and Natural Science Foundation of China (Grant No. 31471623 and 21276154).

Authors’ contributions

Gu X. Z. and Yu S. D. designed the study, carried out the

experiment and wrote this manuscript. Wu Q.Y., Gong S. X.

and Wu J. H. gave some suggestions for this research. Wu J. H.

and Wang Z. W. drafted the manuscript. All authors reviewed the manuscript.

References

Acree, T. and Arn, H. (2004). Flavornet: Gas chromatography- olfatography (GCO) of natural products. Cornell University. http://

flavornet.org/flavornet.html

Beullens, K., Mészáros, P., Vermeir, S., Kirsanov, D., Legin, A., Buysens, S., Cap, N., Nicolaï, B. M., and Lammertyn, J. (2008).

Analysis of tomato taste using two types of electronic tongues.

Sensor Actuat. B: chem., 131, 10‒17.

Cao, Y., Zhang, F., Zhang, T., Chen, S., and Li, H. (2019).

Optimization of fermentation process for potato pulp steamed bread by response surface methodology. Food research and development, 40, 32‒39. (in Chinese with English abstract)

de Wijk, R. A., Smeets, P. A. M., Polet, I. A., Holthuysen, N. T. E., Zoon, J., and Vingerhoeds, M. H. (2018). Aroma effects on food choice task behavior and brain responses to bakery food product cues. Food Qual. Prefer., 68, 304‒314.

Feng, Y., Cai, Y., Fu, X., Zheng, L., Xiao, Z., and Zhao, M. (2018).

Comparison of aroma-active compounds in broiler broth and native chicken broth by aroma extract dilution analysis (AEDA), odor activity value (OAV) and omission experiment. Food Chem., 265, 274‒280.

Filly, A., Fabiano-Tixier, A. S., Fernandez, X., and Chemat, F. (2015).

Alternative solvents for extraction of food aromas. Experimental and COSMO-RS study. LWT-Food Sci. Technol., 61, 33‒40.

Gu, X., Sun, Y., Tu, K., and Pan, L. (2017). Evaluation of lipid oxidation of Chinese-style sausage during processing and storage based on electronic nose. Meat Sci., 133, 1‒9.

John, C. (2007). “Flavor-Base (Demo) (7th edn.).” Georgia, Leffingwell & Associates.

Kano, M., T. Takayanagi, K. Harada, K. Makino, and F. Ishikawa.

(2005). Antioxidative activity of anthocyanins from purple sweet potato, Ipomoera batatas cultivar Ayamurasaki. Biosci. Biotechnol.

Biochem., 69, 979‒88.

Kita, A., A. Bąkowska-Barczak, K. Hamouz, K. Kułakowska, and G.

Lisińska. (2013). The effect of frying on anthocyanin stability and antioxidant activity of crisps from red- and purple-fleshed potatoes (Solanum tuberosum L.). J. Food Compos. Anal., 32, 169‒175.

Li, J., Yuan, H., Yao, Y., Hua, J., Yang, Y., Dong, C., Deng, Y., Wang, J., Li, H., Jiang, Y., and Zhou, Q. (2019). Rapid volatiles fingerprinting by dopant-assisted positive photoionization ion mobility spectrometry for discrimination and characterization of Green Tea aromas. Talanta, 191, 39‒45.

López-López, A., Sánchez, A. H., Cortés-Delgado, A., de Castro, A., and Montaño, A. (2018). Relating sensory analysis with SPME-GC- MS data for Spanish-style green table olive aroma profiling. LWT- Food Sci. Technol., 89, 725‒734.

Miyagusuku-Cruzado, G., N. Morishita, K. Fukui, N. Terahara, and T.

Matsui. (2017). Anti-Prediabetic Effect of 6-O-Caffeoylsophorose in

(10)

Prediabetic Rats and Its Stimulation of Glucose Uptake in L6 Myotubes. Food Sci. Technol. Res., 23, 449‒456.

Nemś, A. and Pęksa, A. (2018). Polyphenols of coloured-flesh potatoes as native antioxidants in stored fried snacks. LWT-Food Sci.

Technol., 97, 597‒602.

Niu, Y., Wang, P., Xiao, Z., Zhu, J., Sun, X., and Wang, R. (2019).

Evaluation of the perceptual interaction among ester aroma compounds in cherry wines by GC–MS, GC–O, odor threshold and sensory analysis: An insight at the molecular level. Food Chem., 275, 143‒153.

Niu, Y., Yao, Z., Xiao, Z., Zhu, G., Zhu, J., and Chen, J. (2018).

Sensory evaluation of the synergism among ester odorants in light aroma-type liquor by odor threshold, aroma intensity and flash GC electronic nose. Food Res. Int., 113, 102‒114.

Qiu, G., Wang, D., Song, X., Deng, Y., and Zhao, Y. (2018).

Degradation kinetics and antioxidant capacity of anthocyanins in air- impingement jet dried purple potato slices. Food Res. Int., 105, 121‒128.

Schranz, M., Lorber, K., Klos, K., Kerschbaumer, J., and Buettner, A.

(2017). Influence of the chemical structure on the odor qualities and odor thresholds of guaiacol-derived odorants, Part 1: Alkylated, alkenylated and methoxylated derivatives. Food Chem., 232, 808‒819.

Song, H. and Liu, J. (2018). GC-O-MS technique and its applications in food flavor analysis. Food Res. Int., 114, 187‒198.

Stafford, L. D. (2016). Olfactory Specific Satiety depends on degree of association between odour and food. Appetite, 98, 63‒66.

Sun, W., Zhao, Q., Zhao, H., Zhao, M., and Yang, B. (2010). Volatile compounds of Cantonese sausage released at different stages of processing and storage. Food Chem., 121, 319‒325.

Xia, Y. (2008). “Food Flavor Chemistry.” Beijing, Chemistry Industry

Press, pp: 23‒57.

Xiao, Z., Chen, J., Niu, Y., and Chen, F. (2017). Characterization of the key odorants of fennel essential oils of different regions using GC–MS and GC–O combined with partial least squares regression.

J. Chromatogr. B., 1063, 226‒234.

Zhang, J., Du, G., Bai, R., Jiang, C., Yang, Z., Li, P., Ou, Y., Cao, F., Tian, S., Jiao, H., Hu, L., Zhu, J., Ma, Y., and Zhou, J. (2018).

Effects of sugar addition on aroma products in the process of burley tobacco roasting. Journal of Hunan Agricultural University (Natural Sciences), 44, 580‒586. (in Chinese with English abstract)

Zhang, W., P. Dong, F. Lao, J. Liu, X. Liao, and J. Wu. (2019).

Characterization of the major aroma-active compounds in Keitt mango juice: Comparison among fresh, pasteurization and high hydrostatic pressure processing juices. Food Chem., 289, 215‒222.

Zhao, B., Zhang, M., and Liang, S. (2017). Effect of Overcooking on Flavor Compounds of Potato. Food Science, 38, 200‒204. (in Chinese with English abstract)

Zhu, J., Wang, L., Xiao, Z., and Niu, Y. (2018). Characterization of the key aroma compounds in mulberry fruits by application of gas chromatography–olfactometry (GC-O), odor activity value (OAV), gas chromatography-mass spectrometry (GC–MS) and flame photometric detection (FPD). Food Chem., 245, 775‒785.

Zhu, Y., Liang, S., Zhang, M., and Yang, Z. (2019). Effect of potato flour with different varieties and types on quality of fresh wet noodles. Journal of Food Science and Technology, 37, 94‒101. (in Chinese with English abstract)

Zhu, Y., Lv, H., Shao, C., Kang, S., Zhang, Y., Guo, L., Dai, W., Tan, J., Peng, Q., and Lin, Z. (2018). Identification of key odorants responsible for chestnut-like aroma quality of green teas. Food Res.

Int., 108, 74‒82.

(11)

Supplementary Fig. 1. The percentage of the volatile compounds belonging to different descriptors in total volatiles of purple potato at different temperatures by GC-MS Refer to Supplementary Fig. 1 at the point of “Identification of volatile compounds by GC-MS”.

(12)

Supplementary Table 1. Aroma-active volatiles detected in purple potato powder at different temperatures by HS-SPME-GC-MS

No. RIa Rtb Compounds Percentage of total area (%) 25 ℃ 40 ℃ 60 ℃ 80 ℃

1 982 15.37 1-Octen-3-ol -c - 1.31 2.20

2 741 8.71 1-Pentanol 3.57 - 4.58 1.65

3 - 41.21 5-Pentyldihydro-2(3H)-furanone - - 2.17 2.76

4 892 14.55 2,5-Dimethyl pyrazine - 3.15 3.31 -

5 895 13.18 2-Heptanone 0.44 - - 0.35

6 1147 30.86 2-Nonenal - - 0.60 0.99

7 - 41.47 2-Butyl-2-octenal - - 1.35 4.50

8 1095 24.81 3,5-Octadien-2-one 1.43 4.24 6.29 11.24

9 829 10.68 Furfural - 2.67 - 1.22

10 1040 17.32 3-Octen-2-one 0.64 1.90 2.94 3.69

11 - 23.79 5-Ethyl-2-furaldehyde - - 0.81 1.19

12 600 4.99 Acetic acid 8.27 32.12 10.40 5.15

13 960 14.96 Benzaldehyde 1.90 4.33 3.00 7.45

14 1049 17.66 Benzeneacetaldehyde 1.52 1.73 4.13 9.77

15 641 5.72 2-Methyl butanal 17.34 - - 2.97

16 650 5.57 3-Methyl butanal 12.26 1.32 0.89 1.90

17 1209 22.54 Decanal 0.80 3.23 2.19 2.43

18 1030 22.03 D-Limonene 0.94 5.21 2.97 0.91

19 993 19.28 2-Pentyl furan 6.36 3.42 4.08 6.22

20 903 13.89 Heptanal - 1.26 1.20 0.91

21 801 9.66 Hexanal 26.34 20.05 16.02 9.77

22 1019 16.57 Hexanoic acid - - 17.02 1.20

23 - 42.85 Longifolene - 1.43 1.73 1.85

24 909 14.26 3-Methional 1.41 - 1.22 -

25 1104 27.23 Nonanal 1.41 10.07 8.45 6.60

26 662 4.52 Isobutyraldehyde 10.74 - - 0.12

27 912 14.53 2,6-Dimethyl pyrazine 3.31 - - 7.46

28 1047 21.28 2-Ethenyl-6-methyl pyrazine 0.65 - 0.71 5.25

29 828 10.22 Methyl pyrazine 0.68 0.98 0.58 0.28

30 911 12.24 Pentanoic acid 0.00 2.89 2.06 -

a: retention index, b: retention time; c: not detected.

Volatiles were identified by comparison of retention index, retention time and MS spectra with the standard Wiley (2011) and NIST (2011) libraries.

Refer to Supplementary Table 1 at the point of “Identification of volatile compounds by GC- MS”.

References

Related documents

Idiopathic VF originating from the RVOT • 16 patients with RVOT VPCs initiating VF or PMVT. • Structural heart

nality of a c-awdp set in G is called the complementary acyclic weak domination preserving number of G and denoted by c-awdpn(G).. In this paper, we introduce and discuss

Step movement for adjunct non-teaching faculty working as librarians, counselors, or in Academic Support Centers (ASC) after initial hire will be contingent on accumulation of

Wraz ze wzrostem sub−MICs, bez względu na rodzaj leku, zmniejszała się liczba bakterii wiązanych na ko− mórkach nabłonkowych.. Przyczyną tego zjawiska były zmiany w

CD68 + 1: CD68-positive macrophages counts in tumor nest; CD68+ 2: CD68-positive macrophages counts in tumor stroma; CD163+ 1: CD163-positive macrophages counts in tumor nest; CD163+

Однако необходимо учитывать , что указанные допускаемые продольные силы являются предельными лишь по условиям выдавлива -. ния вагонов в голове поезда при исправном подвижном