The effect of yeast extract supplementation on activity of bulk starter in cheese manufacturing: A laboratory simulation

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Starter culture plays a crucial role in deciding ultimate flavor, aroma, texture and moisture content of natural cheese. Milk, the traditionally used bulk starter (BS) media for cheese starter growth, is found not to provide all the nutrients for starter culture growth. This study investigated the effect of yeast extract as a BS media supplement in increasing cheese BS activity. The BS system and cheese vats in a selected commercial cheese factory were simulated on laboratory scale. Conditions used in the BS system and cheese vats such as temperature, pH, neutralising agent, starter strains and inoculum sizes were used equivalent to those that are used in the selected cheese factory. Effect of two commercial yeast extracts (YE-A and YE-F) on activity of Lactococcus lactis sub sp. cremoris strains 49, 831, 1926 ASCRC in BS were evaluated. Starter growth during BS fermentation was analysed determining lactic acid (LA) production and pH reduction. Activity of cultures was evaluated by continuous pH monitoring in simulated cheese vats. YE supplementation increased LA production in the BS and reduced fermentation time by 20% compared to traditional BS media. 0.5% YE-A and 0.2% YE-F were chosen as optimum levels for simulated BS. YE supplemented BS cultures were more active compared to no YE added BS cultures, allowing inoculum levels required to inoculate cheese vats to be reduced by 40%.