Lesson 31. MICROBIOLOGICAL QUALITY AND SAFETY ASPECTS OF TRADITIONAL DAIRY PRODUCTS
Module 13. Microbiology of traditional dairy products
Lesson 31
MICROBIOLOGICAL QUALITY AND SAFETY ASPECTS OF TRADITIONAL DAIRY PRODUCTS
Since the production of various indigenous milk products is in the hands of ‘halwais’ (sweet makers) and rural areas, where unhygienic processing conditions are prevalent, the products are grossly contaminated. The contamination results into a considerable increase in the population of spoilage organisms, thereby, lowering the keeping quality of the products. The entry of pathogens which have great significance from the public health point of view is a major issue as the products are consumed by different sections of society including the vulnerable ones.
Dairy scientists have investigated microbiological quality of these products. Efforts are being made to bring improvement in maintaining standards of various indigenous milk products through technological modifications during their production.
31.2 Microbiological Quality of Khoa, Burfi and Peda
Khoa, like other indigenous milk products, can serve as a favourable medium for the growth of a variety of microorganisms due to its high moisture content and good nutritive value. The market khoa usually keeps well for 48 h under usual Indian conditions beyond which it deteriorates due to microbial action. These organisms gain access as contaminants from different sources in to product. The rapid spoilage of khoa is attributed to contamination with moulds from external sources. A number of investigations were carried out by different groups of workers on the microbiological status of khoa and khoa based sweets in different parts of the country.
31.2.1 Types of micro flora
Various groups of bacteria (acid producers, proteolytic, chromogenic, lipolytic, aerobic sporeformers, psychrotrophs, thermophiles, pathogens), yeasts and moulds have been reported to occur in khoa.
Psychrotrophic bacteria mainly Pseudomonas, Achromobacter, Flavobacterium and Alcaligenes, have been isolated from peda. On the basis of comparative analysis of khoa, burfi and peda, khoa contained higher population of yeasts and moulds than burfi or peda.
The composite microflora of market burfi and peda was studied in which bacteria, yeasts and moulds were isolated from both the products, though the proportion of yeasts and moulds was extremely low as compared to bacteria. Among the bacteria, Gram-positive (mainly cocci) predominated in both the products.
Table 31.1 Microbial Quality of khoa/chhana/paneer as per FSSA rules
31.2.2 Microbiological quality of paneer
The microbiological quality of paneer, like other indigenous milk products, chiefly depends on the conditions of manufacture, subsequent handling, storage and sale of the product. The possible sources of contamination might be air, water, utensils, cutting knife, muslin cloth as well as persons handling the product. Hence, the number and types of microorganisms and their distribution in the product may vary depending on the location of the halwai shop, extent of exposure of the product to the atmosphere, temperature and period of storage etc. According to a survey conducted on the market quality of paneer obtained from Karnal and Delhi samples were found to contain heavy load of total bacterial population, coliforms and yeasts and moulds. Another study on market paneer from Ludhiana city indicated heavy contamination of the product with Staphylococci, 25% of which were found to be positive for coagulase and TDNase.
31.2.3 Microbiological quality of chhana
Chhana samples showed an average bacterial count of 1.6 x 104 per gram. However, during storage at 37 ºC, the count increased to 31 x 106 and 110 x 106 at the end of 24 and 48h, respectively. The spoilage of the product was chiefly due to thermoduric bacteria. Among the bacterial types isolated from chhana, micrococci predominated and constituted 45 % of the total microflora, followed by sporeformers (34%). The remaining portion (about 27%) constituted non-sporeforming rod shaped bacteria. Incidence of yeasts and moulds was studied and the initial count of 260 per gram increased to 385 x103 per gram on storage for 48 hours. The most commonly occurring moulds in chhana belonged to the genera Penicillium, Aspergillus, Mucor, Rhizopus, Fusarium etc.
31.2.4 Microbiological quality of shrikhand
Analysis of market samples and laboratory made samples indicated that the product was free from coliforms. Quality control test of shrikhand showed not more than 85 x 105 cfu/g for yeast and mould count and absence of coliforms in 0.1 gram of shrikhand. The contaminants may enter the product during centrifuging / straining or subsequent conversion of chakka to shrikhand or through sugar. However, no food poisoning outbreak has been reported so far due to consumption of shrikhand.
Table 31.2 Microbial quality shrikhand of as per FSSA rules
31.2.5 Pathogenic organisms from khoa, burfi and peda
A number of pathogens like Salmonella typhi, Shigella dysenteriae, Vibrio cholerae and E. coli are able to survive for long periods during storage of khoa. Subsequently, a number of related studies have revealed the occurrence of staphylococci, especially those of heat stable, coagulase positive, enterotoxin producing types in khoa, burfi and peda. Drug resistant coliforms and enteropathogenic E. coli have also been isolated from khoa. Although coliforms are heat labile, their isolation from large samples of the product indicates post-processing contamination. The presence of coliforms may also indicate the likely presence of potential pathogens like Salmonella, Shigella etc. in the product. Contamination of khoa, peda and burfi with Salmonella schottmuelleri and Shigella flexneri has also been found to correlate with faecal contamination. It was proved that S. aureus, a potent food poisoning organism, can multiply in khoa, peda and burfi at the ambient storage temperature as well as at 37 ºC.
31.3 Spoilage of Indigenous Products by Microorganisms, Control Measures
The constituents of khoa and its sweets facilitate the multiplication of different surviving as well as contaminating micro-organisms, capable of causing the following defects as a result of their growth and activity.
31.4 Microbiological Defects in Khoa
31.4.1 Rancidity
On storing khoa under ambient conditions, the fat component is degraded by the action of microbial lipases. Such lipases are produced by certain lipolytic bacteria, yeasts and moulds. Both hydrolytic as well as ketonic rancidity might be produced depending on the nature of microbial activity.
31.4.1.1 Control measures
Storage of khoa under refrigerated conditions (below 10ºC) coupled with general hygienic measures during production are advisable.
31.4.2 Stale and sour flavour
These off-flavours are produced mainly due to the activity of proteolytic and acid producing organisms at relatively lower storage temperatures.
31.4.2.1 Control measures
Post-processing contamination especially through unclean utensils, water supply etc. should be minimized.
31.4.3 Mould growth
Storage of Khoa at ambient and also at relatively lower temperatures might favour the growth of moulds which impart off-flavours and may also produce certain mycotoxins under favourable conditions. The mould growth is favoured by the presence of high moisture content in the product, air leakage in the package, high humidity and sufficient aeration in storage room, etc.
31.4.3.1 Control measures
- Since moulds usually enter the product through aerial contamination, proper sanitation through cleaning and fumigation of the dairy environment would control the problem. Apart from this, mould contamination in the product can also be tackled through control of humidity and aeration in the processing and packaging room.
- The moisture level in khoa should not be allowed to exceed the prescribed limits.
- Khoa should be stored in air-tight packages.
- Treatment of wrapping paper with antifungal agents like potassium sorbate controls mould growth. However, use of such chemicals in the product is not permissible.
Due to high fat and moisture content, these products are prone to microbiological spoilage leading to rancidity (due to fat breakdown) and mouldy surface (due to mould growth). Storage of packaged chhana or paneer at low temperature (5ºC - 10ºC) can check the rancid defect. The mould growth can be avoided by keeping moisture at an optimum level and by avoiding delays in the marketing and disposal of these products.
Last modified: Monday, 15 October 2012, 5:38 AM