Abstract
Introduction. Dairy products are an important part of the diet. Kashk is a traditional Iranian dairy product rich in protein. However, kashk has a high water content and is a good medium for the growth of microorganisms. The aim of this study was to investigate the effect of the ethanolic extract of caper fruit (Capparis spinosa L.) on reducing the microbial burden of kashk.
 Study objects and methods. The study objects were three kashk samples. The control sample was kashk without caper extract. Two experimental samples included kashk with 0.211 and kashk with 0.350 mg/mL of ethanolic caper extract. All the samples were tested for pH, sensory and antioxidant properties, colorimetric parameters, and microbial population. The experiments were performed on days 0, 7, 14, 21 and 28 of storage.
 Results and discussion. The results showed all the samples had pH within the standard values during the entire shelf life (3.96 to 4.53). The samples with 0.350 mg/mL of the caper extract had the lowest EC50 (12.05 μg/mL), i.e. the highest antioxidant activity. The increased concentration of the extract and storage time resulted in a decrease in L* and increase in b*, while did not impact a*. Staphylococcus aureus population increased more rapidly than Clostridium botulinum during the storage time, and the overall sensory acceptability of the kashk samples on days 0 and 7 received the highest score.
 Conclusion. The kashk samples containing 0.350 mg/mL of caper extract had an improved antimicrobial, antioxidant and antifungal properties and can be produced and consumed as a new functional product.
Highlights
Dairy products are an important part of the diet
The results of the study showed that the caper (Capparis spinose L.) extract had no adverse effects on pH of kashk during storage time, and the kashk sample with the extract at the concentration of 0.350 mg/mL had the lowest EC50 (12.05 mg/mL), or the highest antioxidant activity on day 0 of storage
The number of bacteria had gradually decreased in the kashk samples with both concentrations of the extract by the end of a 28-day storage
Summary
Dairy products are an important part of the diet. Kashk is a traditional Iranian dairy product rich in protein. Staphylococcus aureus population increased more rapidly than Clostridium botulinum during the storage time, and the overall sensory acceptability of the kashk samples on days 0 and 7 received the highest score. The kashk samples containing 0.350 mg/mL of caper extract had an improved antimicrobial, antioxidant and antifungal properties and can be produced and consumed as a new functional product. Kashk has a high microbial contamination potential due to its high moisture and protein content, and if contaminated, it can be very dangerous and even lead to fatal cases. This product is mostly exposed to Staphylococcus aureus and Clostridium botulinum contamination [9, 12, 13]
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