Ghee (clarified butterfat), a popular dairy product of the Indian subcontinent, develops off‐flavor during storage due to autoxidation. Addition of rosemary extract (RME), a source of natural antioxidants, @ 0.1%, increased the antioxidant potential of ghee in terms of radical scavenging activity (DPPH assay) without affecting sensory and physicochemical properties. Rancimat analysis at 130 °C revealed that ghee added with RME showed a significantly higher induction period (4.4 hr) than control (1.7 hr). Based on peroxide and TBA value determinations, it was observed that shelf life of ghee added with RME was significantly higher than that of control and ghee added with BHA. Addition of RME has also imparted thermal stability to ghee and delayed the onset of cholesterol oxidation, when used as frying medium. Findings suggested that RME could be used as a source of natural antioxidants for imparting autoxidative and thermal stability to ghee. Practical applications Ghee is a major dairy product in India; about 35% of milk is converted to ghee. Though ghee is high in saturated fatty acid content (∼65%), it has lower shelf life than many vegetables oils, due to a lower level of antioxidants. BHA, a synthetic antioxidant, is permitted to be added in ghee in India. However, the current scientific evidences suggest to use natural antioxidants and avoid the synthetic ones. Our findings have shown that that addition of rosemary extract, a promising source of natural antioxidants, increased the antioxidant potential of ghee and extended its shelf life, without affecting the inherent quality of the product; it also imparted ghee with thermal stability during frying. These observations suggested that rosemary extract could be used as a source of natural antioxidants for imparting autoxidative and thermal stability to ghee.
This study was conducted to evaluate the effect of transglutaminase addition on the rheological and sensory properties of low-fat set dahi. The enzyme was added to low fat milk after preheat treatment at the rate of 5 U/g of protein for cow milk and 3 U/g of protein for buffalo milk. Once desired cross-linkage was obtained, transglutaminase was inactivated by heat before culturing. Transglutaminase treatment resulted in improvement of the rheological and sensory properties of dahi prepared from cow or buffalo skim milk and partially skimmed milk. It improved the water-holding capacity up to 85% in skim milk dahi and up to 90% in partially skimmed milk dahi, and firmness up to 1.1 N in cow skim milk dahi and up to 1.8 N in cow partially skimmed milk dahi; these values were almost double in low-fat buffalo milk dahi. Syneresis, appearance and consistency of the final product were also improved. The high gel strength improved the storage stability of treated dahi at refrigerated temperature up to 2 weeks. PRACTICAL APPLICATIONSDahi is the most important fermented milk product used in India from time immemorial. In Indian system of medicine (Ayurveda), dahi has been strongly recommended for curing ailments like dyspepsia, dysentery and other gastrointestinal disorders. This product is also believed to improve appetite and vitality. Dahi is a very nourishing food. It is available as source of protein, essential vitamins and minerals. It is also a rich source of calcium and riboflavin. We consider the low fat dahi, which provides all the benefits of Dahi without the bad effects of milk fat. As the reduction of fat from milk affects the quality of dahi such as viscosity, gelation, water-holding capacity, etc. Through this study, it was observed that the application of transglutaminase pretreatment is a promising alternative to improve textural properties of low fat dahi. Enzymatic cross-linking of milk proteins results in specific changes in product microstructure; this helps to produce good quality dahi from skim milk or partially skimmed milk.
The performance of the starter culture is a critical factor that decides the quality of fermented milk. Dahi is a fermented milk product popular in India made using a mixed starter culture of lactic acid bacteria comprising acid and flavour producers. The prevalence of bacteriophages in the dairy environment can critically affect the activity of these starter cultures resulting in starter failure. As there is little information available on the occurrence of bacteriophages in the dairy environment of Kerala, this research communication examines the presence of lytic bacteriophages acting against three potential flavour-producing strains of Lacticaseibacillus paracasei (Lc. paracasei). Dairy effluent samples were screened for the presence of phages against the strains of Lc. paracasei by the multiple host enrichment method. Plates showing clearance zone in spot assay were confirmed for the presence of phages by double-layer agar assay. The plaques obtained in the double-layer agar assay were purified for further identification by next-generation sequencing. A bacteriophage infecting one of the three strains of Lc. paracasei was detected by the plaque assay and the blast annotation of the bacteriophage sequence found 86.05% similarity of the phage to Siphoviridae family. The study endorses the need for monitoring phages in the dairy environment to control phage-related starter failure in the state of Kerala.
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