Low cost optimization of the flavor,consistency and keeping quality of fermented milk with particular reference to consumer acceptability in Kenya

Abstract

Fermented milks of differing aroma intensities were tested for acceptability by adult Kenyans. One homolactic culture CH:143, two BD cultures (CH:Ol and CR:02) and one B-CH:40 mesophilic lactic culture were used to ferment reconstituted skim milk (RSM) or fresh skim milk (FSM) of varying total solids levels at room temperature (23+10C) using 1% 18hr culture inoculum. The curd was stirred after 15hrs incubation without prior cooling. The heterolactic B-CH:40 culture gave a product with mild aroma (1 - 2 ppm diacetyl) which was most preferred after 21hr at room temperature. Plain sour milk produced by the homolactic culture CH:143 was the least preferred. The BD cultures produced less viscous product due to high CO2 production and were less preforred. The addition of 2.5 - 2.7% skim milk powder to bring solids level to 11.5% or reconstitution of skim milk powder at the rate of 125 g/l produced desirable product. Fresh skim milk produced a more viscous product with better flavor than reconstituted skim milk irrespective of culture type. The addition of as little as 25% FSH to RSH was adecua t o in improving the flavour and consistency of RSM cultured with B-CR:40. The addition of 0,15% citric acid to RSM increased diacetyl and acetaldehyde levels, but concurrently excess CO2 gas was produc ed by low aroma culture CH: 40,leading to excessive wheying off and less acceptability. Heat treatment of the milk at 75°C for 30 minutes was found adequate for optimum viscosity of cultured RSM using high heat skim milk powder. However, 85oc for 30 min was necessary for RSM containing as little as 25% FSM. Hydrogen peroxide-catalase (PC) treatment at the rate of 0.1-0.2% H202 increased diacetyl levels in 21hr samples to at least 10 ppm, the diacetyl remaining stable for up to 93hrs at room temperature. The resulting 21hr product was much less liked than the control.Acceptability improved considerably and was above the control after 45hrs incubation. From 45hrs to 93hrs incubation it remained stable. Addition of 2% to BF to skim milk did not improve acceptability over skim milk samples. However, fermented milk with 3.4% BF was more preferred than cultured skim milk. The results of the studies indicate that fermented milk of acceptable flavour, consistency and good keeping quality can be produced from good quality skim milk powder reconstituted at the rate of 125 g/l, fresh skim milk reinforced with 2.5% skim milk powder or full fat milk fermented with commercial mesophilic heterolactic cultures of mild diacetyl aroma. In warm countries, where ambient tempeatures coincide with the optimum range of such starter cultures, incubators are not required.The fact that the lactic acid level does not increase beyond I - 1·2% anyway, makes cooling of the sour curd unnecessary.