Traditional Dairy Products

Lesson 6. PACKAGING AND SHELF LIFE OF KHOA; DEFECTS IN KHOA AND USES OF KHOA

Module 2. Khoa

Lesson 6
PACKAGING AND SHELF LIFE OF KHOA; DEFECTS IN KHOA AND USES OF KHOA

6.1 Introduction

In general, khoa can keep well for 2-3 days at room temperature and for a week under refrigerated storage conditions. The shelf life of khoa is mainly dependent on moisture content of khoa, temperature of storage, bacteriological quality of raw milk, hygienic conditions maintained during production, duration of storage, type of package and method of packaging.

6.2 Keeping Quality of Khoa

The limited shelflife of indigenous milk products is one of the main limiting factors in marketing. During storage, these products undergo many types of sensory, rheological, chemical and microbiological deterioration making them unfit for human consumption. Most of the traditional dairy products except ghee have shelflife varying from less than 24 hours to about a week at ambient temperature. Addition of sugar, boiling in sugar syrup or frying is some of the methods which are traditionally adopted to enhance the storage life of these products.

The keeping quality of khoa at room temperature is about 5 days and 10 weeks at the refrigeration temperature. Storage of khoa at low temperature (5-10°C) though enhances the keeping quality, it adversely affects the body and texture and its portability for sweet making. Hence all care should be taken during manufacture and subsequent handling.

The following factors control the keeping quality of khoa (water activity of khoa is 0.960):

• Quality of raw material - Use of poor quality milk particularly sour or neutralized lowers the keeping quality of the final product.

• Quality of khoa - Khoa having high moisture (ideal is 30-50% moisture) content has very poor shelf life. The high amount of fat (30-40%) particularly free fat, in presence of copper and iron is very much favorable for oxidized flavour. Therefore, khoa should not be contaminated with these pre-oxidant catalysts (The ideal moisture)

Manufacturing conditions

Sanitary conditions should be adopted at all stages of manufacture of khoa and its subsequent handling. Minimum is the contamination with micro-organisms, better will be the keeping quality of khoa.

Temperature of storage

Higher the temperature of storage, lower is the shelf life and vice versa.

Temp. of storage Shelf life on days
Unpacked Packed in laminates

5°C ≤ 10 > 30
30°C ≈ 5 6-7
37°C ≈ 3 ≤ 5

At room temperature (24-30°C) a rancid flavour is developed on khoa while at low temperature (5-10°C) a stale and sour flavour is observed and there is mould growth on the surface.

Type of package

Shelf life of khoa is in increasing order, open tray < parchment paper < LDPE < Food grade HDPE < Laminates < Tins

Methods of packaging

The method of packaging is very important in relation to keeping quality of khoa. Packaging of khoa under aseptic environment and selection of an appropriate packaging material improves the keeping quality of khoa.

6.3 Improving Shelf Life of Khoa

6.3.1 Packaging

Under existing trade practice, producers and traders do not employ any packaging for khoa. By employing proper packaging, the shelf life of khoa can be enhanced. Hot packaging of khoa in pre-sterilized cans can improve the shelf life upto 14 days at room temperature and 75 days under refrigerated temperatures. Three times increase in shelf life was claimed by packing khoa in rigid polypropylene containers with lid. Vacuum packaging and packing in Cryovac Shrink wrap pouches will prevent growth of aerobic microorganisms in khoa. However, these two packaging methods do not offer protection against bacteria growing inside khoa.

6.3.2 Thermal treatment

Hot filling of khoa in rigid containers at 85°C is useful in extending the shelf life of khoa. Packaging of khoa in aluminium cans and steaming them for 15 to 20 min will prevent the spoilage for few weeks. Deep freezing of khoa and storing at -10 to -20°C will extend the shelf life for considerably long periods. However, at this temperature of storage, the lactose which is in super saturated state in khoa gets crystallized and gives rise to sandiness defect.

6.3.3 U.V. irradiation

Irradiation of khoa with U.V. rays will preserve the khoa up to 25 days. However, oxidation changes are caused by U.V. irradiation affecting the flavour of khoa.

6.3.4 Chemical preservation

Under Food Safety and Standards regulations, no preservative should be added to khoa. However, some attempts were made to improve the shelf life of khoa by adding mould inhibitors, nisin and antioxidants. Antifungal agents like sorbic acid, propionic acid and their salts can be used to preserve khoa. Addition of 0.2 % sorbic acid by weight of khoa during the last stage of its manufacture will enhance the shelf life up to 20 days at 30°C and 125 days in cold storage. The mould inhibitors can be sprayed on to the surface of the product or alternatively the packaging material can be treated with the chemical agent. Addition of Nisin (Nisaplin) will improve the shelf life of khoa by 10-11 days at 30°C.

6.4 Chemical and Microbial Changes in Khoa During Storage

6.4.1 Chemical changes

• Moisture: Loss of moisture takes place resulting into dry and hard surface of khoa. The extent of evaporation however depends on the temperature of storage and packaging material. The higher the storage temperature the higher is the rate of evaporation. More the water vapour transmission rate (WVTR) of package faster the loss of water from khoa. Minimum loss of moisture takes place in case of tins and maximum loss in parchment paper.

• Acidity: Lactic acidity increases with the storage period. Higher percentage increase take place at higher temperature and vice-versa. The pH normally decreases during storage corresponding to the increase in acidity.

• Deterioration in fat: The peroxide value increases due to oxidative spoilage during storage of khoa, particularly at ambient temperature. The hydrolytic rancidity in khoa take place thereby increasing the free fatty acids measured as % oleic acid.

• Breakdown in milk protein: There is break down of milk protein in khoa as recorded by the increase in tyrosine value.

• Changes in organoleptic quality: The changes in organoleptic quality of khoa during storage include development of off flavour (stale, sour, oxidized, etc) hardening of body and texture and increase in intensity of colour.

• Microbial changes: The hygienic quality of a food product is judged by microbiological analysis for indicator organisms(s) which shows the safety and keeping quality by revealing the sanitation at the place of manufacture and also during processing, marketing, transportation and storage.

• Most of the Indian milk products are almost sterile when fresh, it is the post manufacture contamination and unhygienic handling that makes the microbiological quality far from satisfactory on account of moisture content the storage at high ambient temperatures. Aerobic spore formers, staphylococci and micrococci are the dominant groups and frequent occurrence of coliform and Staphylococcus aureus, salmonella and Bacillus cereus etc. have been reported in indigenous milk products.

Milk is subjected to boiling temperature for a considerably long time (15-20 min), during manufacture of khoa. Therefore except spores all other micro-organisms are destroyed during khoa making. Khoa manufactured by continuous methods in practically sterile when comes out of the machine. On the contrary khoa made by traditional methods contains comparatively high microbial load. Despite high heat treatment, heavy load of all types of microflora has been observed in market khoa samples which are the result of adoption of unhygienic condition and post production contamination. The aerobic spore formers and the moulds are mainly responsible for the microbial spoilage of khoa.

6.5 Defects in Khoa

Defects in khoa arise from inferior quality milk, unhygienic conditions during manufacturing and duration of storage. Some of the common defects observed in khoa are listed below.

Table 6.1 Defects in khoa, causes and prevention

6.6 Uses of Khoa

• Khoa is mainly used in the manufacture of a variety of khoa based sweets like gulabjamun, peda, burfi, kalakand, milk cake etc.

• Khoa is used in the preparation of carrot halwa, palangtod, laddoo etc.

• Khoa is used as a topping for payasam, kaddu ka kheer, other sweets etc.

• Khoa is used for direct consumption after mixing with sugar.

 

Reference:

• Rajorhia, G. S.(2002) Opportunities in production and marketing of khoa and its packaging Proc.XXXI Dairy Industry Conference, Mumbai.pp.51-57.

• Kumar, G. Srinivasan, M. R.(1983) Effect of selected packaging materials and storage on the microbiological quality of khoa. Indian J.Dairy Sci., 36(5): 172-177.