4. DESCRIPTION

The present invention relates to the field of yogurt processing, specifically, shelf-life extension of functional yogurt and preparation methods. In recent years, the health awareness among people is growing and yogurt has been recognized as a nutritious food. Currently, the yogurt has a product shelf-life of only 14-21 days, and needs to be refrigerated. This gives transportation, storage and sale of yogurt a lot of trouble. Therefore, to extend the shelf-life of yogurt is imperative.
FIELD OF INVENTION
This invention relates to a process of extending the shelf life of yogurt as an alternative to conventional products.

BACKGROUND OF THE INVENTION

Curd is an important fermented dairy product used in India as a refreshing beverage. It has mild pleasant flavor, with a clean acidic taste, a creamy white color with a smooth, glossy surface and cream layer on top. The mass of curd is expected to be soft and firm, free from gas holes (Srinivasan, 2011). It is well known that curd cannot be kept for more than 24 hours (16-24°C). On prolonged storage it becomes highly acidic, thus making it unpalatable for human consumption.

Therefore different methods are applied to restrict the growth of spoilage undesirable microorganisms. Research work at National Dairy Research Institute, Bangalore has shown that bottled curd of long keeping quality can be prepared by using selective strains of lactic acid bacteria (LAB) (Ganguly, 2001). LAB shows remarkable antimicrobial activity against pathogens and spoilage microorganisms. This is mainly attributed to the production of some compounds with antimicrobial activity as lactic and other organic acids, hydrogen peroxide bacteriocjns and other low molecular mass compounds with bio-preservative capacity.

OBJECTIVES OF THE INVENTION

A method of pre-freezing technology for extending the shelf-life of fresh lactic yogurt

SUMMARY OF THE INVENTION

The method produces yogurt with extended shelf-life rather the short shelf-life of about 3-4 weeks for the conventional product at refrigerated temperatures. Shelf-life and stability of the yogurt is enhanced facilitating economically feasible commercial production. A number of specialty yogurt manufacturers in India who produce high quality fresh lactic yogurt are keen to further extend the shelf-life of their product to enable them to enter expanding export markets.
However, at the present time the only means of achieving this objective is by using preservatives. As this would be unacceptable to consumer concerns about food additives, manufacturers are therefore keen to find alternative technologies and processing methods to facilitate entry to export markets and without disturbing the sensory attributes and pH of the product.

The objectives and other advantages of this invention will be further understood with reference to the following figures, detailed description and example.

WORKING PROCESS OF THE INVENTION

Fresh lactic yogurt traditionally has short shelf-life of about 3-4 weeks at refrigerated temperatures due to souring and outgrowth of yeasts and moulds towards the end of the storage periods. Microbial inactivation may be achieved at lower pressure levels by decreasing pH, increasing temperature or adding antimicrobial compounds such as bacteriocins, sorbic or benzoic acids, ethanol, spice extracts, lysozyme or chitosan (Karatzas et al., 2001).

The application of HPP (200-500 MPa) combined with other hurdles such as mild heat or the bacteriocins such as nisin or lacticin has been reported to improve the rate of inactivation of indigenous or inoculated micro-organisms, particularly Gram-negative bacteria in milk and fresh cheeses (Black et al., 2010). A similar bio-protective effect of reduced water activity was reported by Molina-Hoppner (2004) for L. lactis by the addition of 2-4 M sodium chloride to the suspending medium.

Haj et al. (2007) reported that when acid production increased, the quality of dairy products is affected based on sensorial characteristics due to sour taste and gas formations. Earlier researchers have found that the population of viable yoghurt organism increased initially after the manufacture and decreased during a long storage period (Damin et al., 2008). The incubation temperature, dissolved oxygen, lactic and acetic acid content in the product, fermentation time, storage temperature are also presumed to affect the viability of probiotic bacteria in dairy foods (Giiler-Akin, 2005).

Quantitative standard bacteria vary from 106-107 CFU/g viable cells as minimum requirements in probiotic products (Damin et al., 2008). The rate of acidification depends on amount and type of starter culture, thus affecting the sequence of gelation and determining the characteristics of casein matrix (Fadela et al., 2009).

Flavour development occurs due to the release of small peptides and amino acids by proteolysis activity (Liu et al., 2010), or due to lipolysis (Casaburi et al., 2008). Lb. delbrueckii subsp. bulgaricus curd had no invertible consistency even at 24 hours, but the mixed curd had a thick invertible consistency till spoilage (72 hours) upto 3 days. Texture results from a complex interaction between milk proteins, acids and exopolysaccharides (Delorme, 2008).

In this invention of ours, the bactericidal activity was performed which is a key factor for considering pre freezing technology for shelf-life extension of fresh lactic yogurt and the potential development of new freeze-treated yogurt based products.

DETAILED DESCRIPTION

Example 1

The raw material formulation comprises of pasteurized milk: 500 mL and starter culture 2%
inoculums. The production method involves fermentation of the formulation mix at 37°C for 3 h.

The optimum fermentation time was taken when the pH reaches 3.5. The yogurt is packed in
containers and subjected to pre-freezing at -20°C for 1 h. The yogurt is stored at refrigerated
temperature (10°C) till consumption.

Example 2

The raw material formulation comprises of pasteurized milk: 500 mL; L. reuteri or S. boulardii:
2% inoculums The production method involves fermentation of the formulation mix at 37°C for 3
h. The optimum fermentation time was taken when the pH reaches 3.5. The yogurt is packed in
containers and subjected to pre-freezing at -20°C for 1 h. The yogurt is stored at refrigerated
temperature (10°C) till consumption.

Example 3

The raw material formulation,comprises of pasteurized milk: 500 mL; L. reuteri or S. boulardii:
2% inoculums and finger millet slurry: 5% of the total weight. The finger millet slurry is prepared by adding water to the finger millet flour in the ratio (1:3) and cooking it till gelatinization and adding to the formulation mix.

The production method involves fermentation of the formulation mix at 37°C for 3 h. The optimum fermentation time was taken when the pH reaches 3.5.

The yogurt is packed in containers and subjected to pre-freezing at -20°C for 1 h. The yogurt is storedat refrigerated temperature (10°C) till consumption.

The number of total bacterial count (TBC), lactic acid bacterial count (LAB) and yeast, mold
counts (YM) were enumerated in the treated yogurt and compared with the untreated yogurt
throughout the shelf-life study.

As seen from the fig. 1 and 2, treated yogurt has maintained optimum pH which is indicative of reduced microbial activity conducive to long-term preservation of yogurt and taking into account the taste, flavor and cost of the yogurt. The corresponding titratable acidity has been recorded.

As can be seen from fig. 3 and 4, the colour and texture of the treated yogurt was not affected during storage when compared to the untreated yogurt. Hence the pre-freezing treatment not only extended the shelf-life of yogurt but also ensures the quality of the yogurt.

As seen from fig. 5, the activity of microbial growth was controlled in the treated yogurt thereby extending its shelf-life than untreated yogurt.

ADVANTAGES OF THE INVENTION

The method achieves a number of advantages over the prior techniques.

1) Enhancing the shelf-life of yogurt (up to 6 months).

2) The nutritional, sensorial and textural properties of the yogurt comply with the conventional product.
PATENT CITATIONS

NON-PATENT CITATIONS
Black, E. P., Hirneisen, K. A., Hoover, D. G., & Kniel, K. E. (2010). Fate of Escherichia coli 0157: H7 in ground beef following high-pressure processing and freezing. Journal of applied microbiology, 108(4), 1352-1360.
Casaburi, A., Di Monaco, R., Cavella, S., Toldra, F., Ercolini, D., & Villani, F. (2008). Proteolytic and lipolytic starter cultures and their effect on traditional fermented sausages ripening and sensory traits. Food Microbiology, 25(2), 335-347.
Damin, M. R., Minowa, E., Alcantara, M. R., & Oliveira, M. N. (2008). Effect of cold storage on culture viability and some rheological properties of fermented milk prepared with yogurt and probiotic bacteria. Journal of Texture Studies, 39(\), 40-55.
Delorme, C. (2008). Safety assessment of dairy microorganisms: Streptococcus thermophilus.
International journal of food microbiology, 126(3), 274-277.
Fadela, C, Abderrahim, C, & Ahmed, B. (2009). Physico-chemical and rheological properties of yoghurt manufactured with ewe's milk and skim milk. African Journal of Biotechnology, 8(9), 1938.
Ganguly N.C. (2001). Carbonation of milk-a process to extend longevity of milk. Indian Dairyman, 53, 29-31.
Guler-Akin, M. B. (2005). The effects of different incubation temperatures on the acetaldehyde content and viable bacteria counts of bio-yogurt made from ewe's milk. International journal of dairy technology, 58(3), 174-179.
Haj, M. H., El Owni, O. A., & El Zubeir, I. E. M. (2007). Assessment of chemical and microbiological quality of stirred yoghurt in Khartoum State, Sudan. Research Journal of Animal and Veterinary Sciences, 2, 56-60.
Karatzas, A. K., Kets, E. P. W., Smid, E. J., & Bennik, M. H. J. (2001). The combined action of carvacrol and high hydrostatic pressure on Listeria monocytogenes Scott A. Journal of Applied Microbiology, 90(3), 463-469.

Liu, M., Bayjanov, J. R., Renckens, B., Nauta, A., & Siezen, R. J. (2010). The proteolytic system of lactic acid bacteria revisited: a genomic comparison. BMC genomics, 11(1), 1. ■
Molina-Hoppner, A., Doster, W., Vogel, R. F., & Ganzle, M. G. (2004). Protective effect of sucrose and sodium chloride for Lactococcus lactis during sublethal and lethal high-pressure treatments. Applied and environmental microbiology, 70(4), 2013-2020.
Srinivasan K. (2011).Traditional Indian Functional foods. In. John Shi, Chi-Tang Ho, Fereidoon Shahidi (ed.). Functional foods of East, CRC Press: Florida.

5. CLAIMS
We claim,

1. A shelf-life extended functional yogurt, wherein said yogurt preparation method comprises the following steps: a) the raw materials are mixed uniformly and packed in containers, b) The set yogurt is subjected to pre-freezing technique c) The treated yogurt is stored at refrigerated temperature (] 0°C) till consumption.

2. The functional yogurt is prepared by
addition of millet to the raw materials.

3. Functionality according to claim 1, wherein said step 2 involves treatment for 1 h at -20°C

4. According to claim 2, the amount of millet added is 5%

5. The method can be extended for preserving butter milk and other similar dairy products.