Optimisation of minimal media for production of aroma compounds typical for fermented milk products

Abstract

U radu je optimirana minimalna podloga na bazi mlijeka i laktoze na kojoj bakterije mliječne kiseline mogu proizvesti maksimalnu količinu hlapivih aromatskih tvari karakterističnih za fermentirane mliječne proizvode. Za pripreme podloga korišten je kazein, tri-natrij-citrat, laktoza, mineralne tvari mlijeka, proteini sirutke i mlijeko s 1,5 % m.m. Glavna razlika pojedinih podloga bila je u količini citrata i proteina sirutke. Fermentacija je vođena pri sobnoj temperaturi do pH vrijednosti 5. Uzorci su senzorski ocijenjeni metodom kvantitativne deskriptivne analize. U svim podlogama željena pHvrijednost, ovisno o količini citrata, postignuta je nakon 68 - 71 sati fermentacije. Fermentacija i nastanak aromatskih tvari bili su intenzivniji u podlogama koje su sadržavale proteine sirutke u usporedbi s podlogama koje su sadržavale samo kazein. Povećana količina citrata u podlogama pozitivno je djelovala na razvoj arome u supstratu. Citrat je povisio početnu pHvrijednost podloge, ali i djelovao kao pufer tijekom fermentacije, zbog čega je bila moguća dulja fermentacija i veća sinteza aromatskih tvari. Pri pH vrijednosti oko 5, aroma karakteristična za fermentirane mliječne proizvode je bila najizraženija, a kiseli okus manje dominantan. Supstrat s 0,25% citrata i 0,1% proteina sirutke, pri pH-vrijednosti 5, imao je najbolje senzorske karakteristike.The aim of this research was to optimize the composition of minimal growth media containing lactose and milk, in which lactic acid bacteria (LAB) would produce the maximum amount of volatile aroma compounds typical for fermented milk products. Ingredients used for the preparation of media were casein, tri-sodium-citrate, lactose, milk minerals, whey proteins and milk with 1.5% fat. The several prepared media differed mainly in the amount of citrate and whey proteins. Fermentation was carried out at room temperature until the media reached pH value of 5. Samples were evaluated for sensory characteristics using quantitative descriptive analysis (QDA). In all media the target pH was reached after 68-71 hours of fermentation, depending on citrate level. Fermentation and the production of aroma compounds were more intensive in media that contained whey proteins compared to media with only casein. Increased citrate level had a positive influence on the aroma production. Citrate increased the initial pH of the media and acted as a buffer during fermentation, which lead to longer fermentation and prolonged production of aroma compounds. At pH around 5, the desired cultured aroma was the most intensive, whereas sour taste was less dominant. The substrate with 0.25% citrate and 0.1% whey proteins, at pH 5, was rated as best regarding its sensory characteristics