FIELD OF INVENTION
The present invention relates to the field of processing of curd and more specifically relates to extending shelf life and stability of curd.
BACKGROUND
Curd is a healthy, universally useful food formed by lactic fermentation of milk. Curd is known for its smoothness and its pleasant and refreshing taste. It is a highly versatile, health promoting and valuable therapeutic food. It is one of the fermented milk products containing characteristic bacterial cultures such as Lactobacillus bulgaricus and Streptococcus thermophilus. However, the problem with curd is that it has a very short shelf life as it becomes excessively sour for human consumption with in few days. There have been attempts to control the lactic acid level to make the curd stable with longer shelf life.
Edwards (US Patent No. 3,432,306) explained a process for preparing chemically acidified milk products and briefed about the disadvantages associated with acidification include the difficulty of controlling the bacterial culture and of protecting the culture from bacteriological contamination.
Povey Robert and Mone Patrick (US Patent 3969534) has developed shelf-stable fermented low-fat dairy products with natural characteristics in plain and flavored varieties with an extended period of retention time, involving syneresis and pasteurization.
From the available literature it is evident that for the retention of the lactic acid bacteria to maintain a high viable cell count in the final product on storage refrigeration is important and hence customarily made curd sold as fresh dairy 2
product in the market is stored under refrigeration though it has very short shelf life.
SUMMARY OF THE INVENTION
The present invention provides a method for extending shelf life of curd and a processed curd obtained by the said method.
In one aspect of the present invention, a method to extend shelf life of curd having steps of homogenizing freshly prepared curd from milk, subjecting the homogenized curd Pulse Electricity Field (PEF) processing, packing the PEF treated curd in pouches made of multilayer flexible packaging materials, permitting the packed curd to remain in water bath, and cooling the packed curd.
In another aspect, curd with extended shelf life obtained through the method steps of homogenizing freshly prepared curd from milk, subjecting the homogenized curd Pulse Electricity Field (PEF) processing, packing the PEF treated curd in pouches made of multilayer flexible packaging materials, permitting the packed curd to remain in water bath, and cooling the packed curd.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides for a method to extend shelf life of curd, including following steps:
homogenizing freshly prepared curd from milk;
subjecting the homogenized curd Pulse Electricity Field (PEF) processing;
packing the PEF treated curd in pouches made of multilayer flexible packaging materials;
permitting the packed curd to remain in water bath; and
cooling the packed curd.
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In the present invention, the curd is prepared by inoculating milk the with curd culture having bacteria as Lactobocillus bulgaricus, Lactobacillus acidophilus, and Streptococcus thermophilus.
The freshly formed curd is homogenized for 3 – 4 minutes and subjected to Pulsed Electric Field (PEF) processing using Pulsed Electric Field generating system at a flow rate of 40 liters/h and a known quantity (200g) is packed in pouches made of multilayer flexible packaging materials such as, but not limited to, Polyester, Aluminium foil, Nylon, and Cast Polypropylene.
The PEF processed and packed curd is kept in a water bath which is maintained at 50 oC - 60 oC for 25 to 40 minutes and later the packed curd was cooled at temperature of <10 oC for a duration of 50 – 60 mintues. The exposure to PEF process injures micro-organisms present in the curd and hence become inactive. The heat treatment followed after PEF process results in the killing of injured hetero-fermentor (gas former) and mesophilic micro-organisms present in the curd due to their low decimal reduction time (D-value). Further, the injured thermophilic bacteria which have relatively higher decimal reduction time (D-value) proliferate survives the exposure to heat treatment , however such thermophilic bacteria have registered a very slow fermentation at room temperature which is confirmed by periodically monitoring the increase titratable acidity of the curd.
The method produces stabilized curd, which is stable and acceptable for human consumption up to three weeks under ambient temperature (28 oC ± 4 oC) and six months at refrigerated conditions (4 oC -5 oC), where the titratable acidity of the curd is found to increase from 0.8% to 1.2% only.
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According to the present invention, the growth of lactic acid bacteria used for the preparation curd may be selectively inactivated by PEF treatment followed by mild heat treatment.
The present invention is explained further in the following specific example which is only by way of illustration and is not to be construed as limiting the scope of the invention.
EXAMPLE:
About 10 liter of cow milk was boiled for 10-15 minutes. After boiling the milk was allowed to cool to temperature of 400C. Once the milk temperature cooled down to 400C it was inoculated with curd culture (mixture of lactic acid bacteria comprising Lactobacillus bulgaricus, Lactobacillus acidophilus and Streptococcus thermophilus) and the mixture (curd culture + milk) was allowed to ferment till a minimum titratable acidity (approximately 0.8 to 0.85 %) with tangy flavor and texture was attained. This process normally takes three to four hours. The freshly prepared curd was homogenized by stirring for a duration of 5 minutes.
The whole lot of homogenized curd was divided into 4 lots, the first lot had 1 liter of the homogenized curd which was kept at room temperature without subjecting to any treatment (control - C). The second lot had 3 liters of the homogenized curd and subjected to Pulsed Electric Field (PEF) processing using Pulsed Electric Field generating system at a flow rate of 40 liter/h (T1). The third lot had 3 liters of the homogenized curd and subjected to mild heat treatment (T2). The fourth lot had 3 liters of homogenized curd and subjected to Pulsed Electric Field (PEF) processing using Pulsed Electric Field generating system at a flow rate of 40 liter/h combined with mild heat treatment at 550C for 30 minutes (T3).
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A known quantity (200g) of all the samples (C, T1, T2 and T3) were packed in pouches made of Aluminum foil. The packed products (T1, T2 and T3) were cooled so as the final product temperature was <100C and all the pouches were stored at room temperature as well as in refrigerated condition. The change in the acidity of the stored product was periodically analyzed at an interval of 24 hours. The acidity of the control sample (C) and sample subjected to mild heat treatment (T2) had attained 1.2% within 36 - 40 hours, whereas in Pulsed Electric Field (PEF) processed sample (T1) acidity was found to reach 1.2% within 60 – 66 hours. In the case of PEF + heat treated samples (T3) the acidity is found to reach 1.2% after 21 days at ambient condition and six months under refrigerated condition and till this time the product was found to have retained tangy curd flavor. Further, the sensory attributes of this stabilized curd is excellent up to 21 days at ambient temperature and six months at refrigerated conditions (40C - 50C).
The present invention provides a very efficient and cost effective method to increase shelf life of curd, which drastically reduces the wastage of curd and adds value to the same. The increase in shelf life will also result in boosting sales of the curd.
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We Claim:
1. A method to extend shelf life of curd, comprising:
homogenizing freshly prepared curd from milk;
subjecting the homogenized curd Pulse Electricity Field (PEF) processing;
packing the PEF treated curd in pouches made of multilayer flexible packaging materials;
permitting the packed curd to remain in water bath; and
cooling the packed curd.
2. The method as claimed in claim 1, wherein the freshly prepared curd has a minimum titratable acidity of 0.8% with tangy curd flavor and texture.
3. The method as claimed in claim 1, wherein the curd is homogenized for a duration of 3 to 5 minutes.
4. The method as claimed in claim 1, wherein the PEF processing is performed using Pulsed Electric Field generating system at a flow rate of 40 liters/hour.
5. The method as claimed in claim 1, wherein the packaging material for preparing the pouches is selected from a group consisting polyester, aluminum foil, nylon, and cast polypropylene.
6. The method as claimed in claim 1, wherein the packed curd remains in water bath for a duration of 30 minutes where the water bath is maintained at a temperature of 50 oC to 60 oC.
7. The method as claimed in claim 1, wherein the packed curd remains stable and acceptable for human consumption for three weeks under ambient temperature of 28 oC to 4 oC and six months under refrigerated conditions.
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8. The method as claimed in claim 1, wherein the curd is prepared by inoculating the milk with curd culture consisting Lactobacillus bulgaricus, Lactobacillus acidophilus, and Streptococcus thermophilus which are pro-biotic in nature.
9. The method as claimed in claim 1, wherein the packed curd is cooled at temperature less than 10oC for a duration of 50 – 60 minutes.
10. Curd with extended shelf life obtained through the method of claim 1.
Dated this the 10th day of September 2013