Current processing methodologies; Pasteurisation

Pasteurisation is a thermal process widely used in the food and dairy industry to extend shelf life and importantly to minimize health risks from pathogenic microorganisms associated with milk. There are several time-temperature combinations to pasteurise milk, which range from 63°C for 30 minutes (LTLT) or 72°C for 15 seconds (HTST) (Fox & McSweeney, 1998; Ranjith, 2000; Grant et al., 2002; Kessler, 2002). As for UV radiation, heat resistance of microorganisms and

resulting pasteurisation efficiency will be determined by a number of factors. These include, but are not limited, to the following: The type of microorganism; the optimal growth temperatures of the microorganism; the cellular lipid content of the microorganism (i.e. an increase in lipid content increases heat resistance of the organism); the tendency of the microorganisms to form clumps and/or clusters (which will increase heat resistance of the colonies or population); the growth stage of the microorganism (microorganism in the logarithmic growth stage will be more heat resistant); the chemical and biochemical composition of the environment or liquid being treated, the pH of the environment (heat resistance will decline as there if outside the optimum pH range of the microorganisms); and the water activity of the food pasteurised (in general there would be a decrease in heat resistance with a decrease in water activity). During refrigerated storage of pasteurised milk, growth of thermoduric bacteria that survives pasteurisation, as well as microorganisms introduced post pasteurisation can reduce the shelf life of fluid milk. The thermoduric microorganisms include Gram-negative (Pseudomonas spp.), Gram-positive (Paenibacillus amylotylicus) bacteria as well as spore forming bacteria (Rossitto et

al., 2012).

In order to regulate and control the quality of raw milk and to limit the risk of bacterial and possible pathogen contamination, each country enforces regulations defining acceptance criteria for raw milk to be used for further processing. For example, in in South Africa the legal specification for the acceptance of raw bulk milk for further processing according to the “Regulations Relating to Milk and Dairy products” (published under Government Notice No. R. 1555 of 21 November 1997) are indicated in Table 2.11 (Anonymous, 1999).

In addition to the regulations relating to acceptance parameters for raw milk, there are also specific regulations relating to the microbiological quality and safety of the final product produced. In regards to pasteurisation the Grade “A” Pasteurised Milk Ordinance (PMO) in the United States governs pasteurised milk quality (Anonymous, 2009). The U.S. Code of Federal Regulations (CFR) (21CFR 131.3) and the PMO for the treatment of milk specify the time and temperature requirements for the reduction of Coxiella burnetii and Mycobacterium tuberculosis (Enright et al., 1957; Jay 1996). However, both the CFR and the PMO address the possibility for processing

alternatives to heat treatment (21 CFR 1240.61 and CFSAN, 2002). In this regard it is important to note that the PMO states “that nothing shall be construed as barring any

other pasteurisation process which has been recognized by the Food and Drug Administration to be equally efficient and which is approved by the regulatory agency" (CFSAN, 2002).

Table 2.12: South African Regulations Relating to Milk and Dairy products: Regulations regarding sale of raw milk for further processing

Parameter Specification

Antibiotics Absent

Pathogenic organisms, extraneous matter or inflammatory products Absent

Clot-Boil test Negative

Standard Plate Count (cfu.mL-1) < 200,000

Coliform bacteria (cfu.mL-1) < 20

Escherichia coli (cfu.mL-1)ii Absent

Escherichia coli (cfu.0.01mL-1)iii Absent

Somatic cell count.mL-1 iv < 500,000

Alcohol Test (68% ethanol v/v) Negative

Published under Government Notice No. R. 1555 of 21 November 1997.

ii

Modified Eijkmann Test

iii

VRB Mug Agar Method and dry hydrated film method

iv _{The Standard Method for Counting Somatic Cells in Bovine Milk is set forth in International Dairy}

Federation (IDF) Bulletin No. 114 of 1979.

The European Union specifies that the processing conditions relating to pasteurised milk requires the milk to be heat treated at a minimum of at least 72°C for 15 seconds according to Regulation (EC) 2074/2005 (Collins et al., 2000). Although the regulation requires 72°C for 15 seconds as the legal minimum the standard dairy practice is to raise this to 72°C for 25 sec as recommended in the Dairy UK Code of Practice on HTST pasteurisation. This increase in temperature is related to the survival of thermoduric Mycobacterium avis subsp. paratuburculosis, which has been linked to Crohn’s disease. Research conducted by Grant et al. (2002) reported that

Mycobacterium avis subsp. paratuberculosis may survive the minimum heat

treatment required by EU Regulation (EC) 2074/2005 (Collins et al., 2000; Grant et

In South Africa the regulation relating to pasteurised milk, specifies that milk needs to be pasteurised at 63°C for 30 minutes (LTLT) or 72°C for 15 seconds (HTST), and the resulting quality and microbiological control parameters specified following pasteurisation are indicated in Table 2.12 (Anonymous, 1999).

Table 2.13: South African Regulations Relating to Milk and Dairy products: Regulations regarding sale of pasteurised milk.

Parameter Specification

Antibiotics Absent

Pathogenic organisms, extraneous matter or inflammatory products Absent

Clot-Boil test Negative

Standard Plate Count (cfu.mL-1) < 50,000

Coliform bacteria (cfu.mL-1) < 10

Escherichia coli (cfu.mL-1)ii Absent

Escherichia coli (cfu.0.01mL-1)iii Absent

Phosphatase Test1 iv Negative

Alcohol Test (68% ethanol v/v) Negative

Published under Government Notice No. R. 1555 of 21 November 1997.

ii

Modified Eijkmann Test

iii

VRB Mug Agar Method and dry hydrated film method

iv

Aschaffenburg and Mullen phosphate test

As far as the chemical and biochemical composition is concerned, HTST pasteurisation will affect some of the components in milk, however, these changes will be directly correlated to the severity of heat treatment and time of heating. The denaturation of proteins is mainly restricted to the denaturation of the whey proteins, excluding α-lactalbumin, which is relatively heat stable. Furthermore, no breakdown of peptide linkages would occur, and as a result casein is considered as a thermal- resistant compound. Renner (1986) reported that denatured proteins are more digestible than their naturally occurring form, because the protein’s structure has changed, resulting it to be more accessible to digestive enzymes. Beddows & Blake (1982) further confirmed that pasteurisation does not impair the nutritional quality of milk fat, calcium, and phosphorus nor does it affect fat-soluble vitamins (A, D, and E) and water-soluble vitamins (B-vitamins, riboflavin, pantothenic acid, biotin, and niacin). The losses of vitamins caused by pasteurisation, such as thiamin (< 3%),

pyridoxine (0–8%), cobalamin (< 10%) and folic acid (< 10%) are considered lower than those that take place during the normal handling and preparation of foodstuffs at home (Lund, 1982). Most of the vitamin C is lost during handling, pasteurisation, packaging, and oxidation of milk. Renner (1986) further reported that about 70% of the remaining vitamin C and 90% of riboflavin could be destroyed by sunlight exposure during storage. In Table 2.13 some of the major changes in milk constituents are summarized following different levels of heat treatment.

Table 2.14: Comparison between HTST, ESL / extended HTST and UHT pasteurisation and the resulting effect on some of the milk components following heat treatment.

Characteristic HTST Pasteurisation ESL / extended HTST UHT

Heating temp. and time 72°C for 15 seconds 120 – 135 °C for 4 – 1 seconds 135 – 145 °C for 10 – 2 seconds Heat enzyme inactivation index Phosphatase negative Peroxidase positive Phosphatase negative Peroxidase negative Phosphatase negative Peroxidase negative Storage conditions Refrigerated Refrigerated Ambient

Type of packaging Clean Ultraclean / Aseptic Aseptic Average shelf-life 8 – 14 days 30 – 60 days 6 – 12 months

Lactulose (mg.l-1) 0 20 – 40 Gallmann, (2000); Ranjith, (2000) 80 - 500 Furosine (mg.g-1) of protein) 0 200 Fredsted et al., (1996) 400 – 1200 Gallmann, (2000) α-Lactalbumin denaturation (%)a ~ 5 ~ 5 Fredsted et al., (1996) ~ 30 – 80 Elliott et al., (2005) β-Lactoglobulin denaturation (%)b ~ 13 Fredsted et al., (1996) ~ 22 Fredsted et al., (1996) ~ 60 – 100 Elliott et al., (2005) Burton, (1988) Immunoglobulin denaturisation (%) ~ 67 Fredsted et al., (1996) ~ 100 Fredsted et al., (1996) ~ 100 Elliott et al., (2005) a

Assuming the concentration of α-Lactalbumin is 1,200 mg.l-1 in the raw milk

b