STARTER CULTURES AND FERMENTED MILK PRODUCTS

Lesson 27. PROBIOTIC PRODUCTS, PRODUCTION FLOW DIAGRAMS AND EFFECTS OF PROCESSING ON MICROBIOLOGICAL QUALITY

Module 15. Probiotics, acidophilus and bifidus milk products

Lesson 27

PROBIOTIC PRODUCTS, PRODUCTION FLOW DIAGRAMS AND EFFECTS OF PROCESSING ON MICROBIOLOGICAL QUALITY

Introduction

Milk and dairy products have been used as the base material for manufacture of majority of probiotic products as milk is has an excellent nutritional value. Among the probiotic cultures, Lactobacilli and Bifidobacteria are enjoying GRAS status and are considered as the most promising microbes for manufacture of probiotic and synbiotic products. This is basically because the selected species of these groups are autocathonous to the intestinal tract and hence can give the maximum advantages in the host. Hence, most of the probiotic products in the market are milk based and are prepared using Lactobacilli and/or Bifidobacteria.

Types of Products

The traditional acidophilus milk is sour,non-pleasant and having rather medicinal type flavour. Bifidobacteria produce more of acetic acid than lactic acid and hence they also give a vinegar type flavour in the basic product. Further, as both these cultures are slow growers in milk, the initial milk used in their preparation is severely heated. That makes it almost sterile so that the chance of survivors overgrowing during incubation can be avoided. This milk also give a cooked type of flavour to natural Acidophilus or Bifidus milk. These limitations did not make these products popular. However, increasing number of reports on their heath benefits, tempted the scientists to develop alternate technologies to make these products more palatable or acceptable. This was overcome by 2-3 different approaches.

1. Not to ferment- The growth and flavour problems were coming when the milk was allotted to fermented. This can be avoided by not fermenting milk. That lead to development of non-fermented products, that contained only viable cells of these organisms in chilled milk.
2. Blending with other bacteria- To enhance the flavour it was thought to supplement additional microflora as starter culture that give good flavour.
3. Concentration and Drying – This changed the form of consumption and improved the shelf-life.
4. Carry acidophilus and bifidus in other popular products.

Based on these concepts number of products has been developed, which can be grouped as under:

1. Traditional fermented products

• Acidohpilus Milk (sour)
• Bifidus Milk

2. Non-fermented milks

• Acidohpilus sweet milk

3. Blending with yoghurt cultures

• Acidophilus yoghurt
• ACO yoghurt
• Acidohpilsbifidus yoghurt
• Bioghurt
• Bifighurt

4. Blending with other cultures

• Acidophilin
• Acidophilus yeast milk

5. Concentrated products

• Acidophilus cream
• Acidophilus paste

6. Dried Products

• Acidophilus powders
• Infant/Baby foods
• Tablets
• Capsules

7. Blending in other products

• Acidophilusice cream
• Probiotic cheese
• Probiotic fruit juices

Following is the brief description of production methods and effect of different processing steps on quality and microbiology of the product taking example of acidophilus milk.

Acidophilus Milk

Acidophilus milk is a sour product that has been allowed to ferment under conditions that favour the growth and development of a large number of Lactobacillus acidophilus organisms. This acidophilus milk is considered as a probiotic since it aids in the well being of the consumer. Acidophilus milk differs from Indian dahi or curd in body, texture, consistency,flavour, chemical composition and in antibacterial activities.

Manufacture of Probiotic Acidophilus Milk

Acidophilus sour milk, as the name indicates, is a sour milk beverage made out of standardized milk by acidifying it with pure culture of acidophilusrods. The steps involved in its manufacture are given in Figure 1.

The acidophilus milk thus obtained is sour with 1 to1.25% lactic acid and pH 3.7 - 4.0. The product should contain more than200-300 million viable L. acidophilus organisms per ml, which possess satisfactory antibiotic effect against E.coli as well as other pathogenic and non-pathogenic undesirable bacteria of the intestinal tract. The viability of the organism is of primary importance in the use of the acidophilus milk.

Effect of processing steps on quality of the product

Each of the processing steps shown in Figure 1 affects the quality of the product and probiotic microflora in it. The manufacturing technology is centered at the‘care of culture’. The selection of raw material, processing conditions, environment, storage, etc. should be decided in such a way that the culture exhibits predictable behaviour and probiotics are available in maximum viable numbers. .

Selection of Raw Milk

The basic principle to be kept in mind is that ‘good quality raw material can give good quality end products’. The raw milk selected here is meant for allowing the growth of live microorganisms. It must support good growth of the culture. It should be fresh, have normal composition,free from mastitis, free from antibiotics and other inhibitors, free from off-flavours and should have low bacterial count. Buffalo milk should be preferred for set types of product as it gives firm curd while cow milk may be good for stirred product, which will be smoother and uniform.

Pretreatments to milk

Pre warming of milk to about 45 C is required to facilitate filtration/ clarification to remove extraneous matter from milk. The manufacturer has to standardize the milk to meet legal requirements for fat and SNF (Solids-not-fat). Technologically, good quality set product is obtained from the milk having 13-15% total milk solids. Fat do not have significant role to play infermentation, but contributes to integrated pleasant flavour and richness to the product. About 3% fat is sufficient to have good quality product, while SNF can be increased to 10-12%, preferably by concentration or by supplementation with skim milk powder.

Heat Processing

The milk intended for fermented product manufacture is generally heated to 80-85°C for30 min. or 90-95°C for 5-10 min. However,the milk for acidophilus milk manufacture is nearly boiled. This higher heat treatment is useful from many angles to the product. It supports good growth of the culture as it destroys other competing microflora, inactivates many other natural inhibitory substances in milk, drives out oxygen and also produce some growth stimulating agents in milk. Higher heat treatment also improves gel stability, thereby reducing the problems of whey separation in the curd.

Cooling

Just after heating, the milk is cooled to incubation temperature, which is around 37-40°C for acidophilus cultures. Adding culture in hot milk destroys the culture.

Inoculation

The tempered milk is inoculated with 1-5% of active culture of Lactobacillus acidophilus. The exact rate of inoculation depends upon the type of culture.

Incubation

After adding culture in the milk, it is uniformly mixed without aeration. It is then incubated in bulk or in the same tank, if stirred product is to be made. If set-product is required, the milk is filled in retail containers before incubation. Incubation is purely a biological process during which the culture grows and brings necessary transformations in milk to get a desirable fermented product. In general, incubation temperature should be kept around 37°C. However, precise temperature of incubation can be determined based on the strains of the culture and their combination used in the product. The period of incubation varies between 4-16 h, depending upon the rate of acid production by the culture in the milk. However, the best end point to stop fermentation is just after the milk sets. Setting takes place at about 0.6% acidity and the remaining acidity required in the product can develop while cooling. During incubation, the milk is very sensitive to mechanical disturbances and other changes. Hence, it should not be disturbed.

Cooling

As soon as the curd sets or desired acidity in the product is achieved, it must be cooled. The rate of cooling affects the quality characteristics of the product and should be decided according to the per cent lactic acid expected in the final product. Rapid cooling may lead to more contraction of gel and separate more whey, while too slow cooling may sour the product. In thermophilic cultured products, two stage cooling is preferred, i.e. in first stage cooling from 40°C to 20°C and in the second stage from 20°C to 5°C in cold store.

In the stirred products, cooling and stirring are simultaneously done. It is advisable to stir the product at lower temperature to reduce the problems of wheying-off. In most cases, the product is stirred at about 20 C and also blended with colour, flavour, fruits, nuts and other additives and then packed in retail containers. The product is to be stored at less than 5°C,until its consumption.

The stirred product can be packed in consumer convenient sizes in attractive cups,polyethylene pouches or cartoons. However, the packaging material used, should be thoroughly sanitized so that it does not add spoilage microorganism to the product. The distribution should always be through cold-chain.

At all times care must be taken to see that sufficient level of live probiotic cells are present in the product upto the end of shelf-life.