Extending the Shelf Life of Traditional Curd Cheese With Indigenous L. Lactis Immobilized on Acid whey Protein and Apple Pomace Matrix

Abstract

Recently, consumers are increasingly interested in healthy and sustainable dairy products. Therefore, we used acid whey protein and a bioactive apple pomace matrix as carriers for indigenous protective L.lactis incorporated into traditional sour milk cheese to extend its shelf life and increase its biological value. The curd (control) was produced in a local dairy; the ricotta-like protein matrix was prepared from the by product - sour whey - and used as a carrier for the indigenous L. lactis LL16 strain [1]. The matrix was immediately mixed into the curd, replacing 20% of it (experimental cheese 1). The other part of the matrix was enriched with freeze-dried apple pomace powder (experimental cheese 2), which was obtained from the Lithuanian Research Centre for Agriculture and Forestry. All cheeses were placed in muslin bags, pressed and later vacuum packed in flexible film. Acidity (pH) of cheese and bacteria (mesophilic lactic acid (LAB, LST ISO 15214:2009), lipolytic and proteolytic [2]. The total number of yeasts and moulds was determined according to LST ISO 21527- 1:2008, and the number of monocytogenic listeria (LST EN ISO 11290-1:2017) and coagulase-producing bacteria (LST EN ISO 6888-1+A1:2005) was determined on the first, eighth, 15th, and 21st days of storage. (The acidity of the control cheese increased (p < 0.05) at the beginning of the study and then decreased (p < 0.05), remaining higher than that of the experimental cheeses throughout the study. Storage time had no significant effect on the acidity of the experimental samples. Proteolytic, coagulase-producing bacteria and listeria were not detected throughout the storage period. The number of LAB was highest in the control cheese and in the cheese with L. lactis LL16 at the beginning of the study. Later, their content decreased in the control sample compared to the experimental cheeses and remained low until day 21 of the study (p < 0.05). The content of LAB in the experimental cheeses also gradually decreased (p < 0.05) as in the control sample, but in the cheese with apple pomace powder an increase of these bacteria was observed, exceeding the level of day 1 on the last day (p < 0.05). Although more lipolytic bacteria had invaded the experimental cheeses (p < 0.05) with the carrier, the supplement with L.lactis LL16 reduced their number to the level of the control cheese from day 10. Moulds were found in all cheeses only on the first day of the study, with no significant differences between samples. Although yeast counts were highest in the experimental cheeses at the beginning of the study, higher yeast counts were observed in the control cheeses from day 15 of storage. In conclusion, the supplementation of traditional curd cheese with indigenous L. lactis LL16 can effectively control the growth of yeasts and lipolytic bacteria. The addition of apple pomace powder to the carrier supports LAB survival in cheese.