Certain Factors Affecting the Concentration of Active Sulfhydryl Compounds in Heated Cream

Open Access
Publisher Website
Google Scholar
Abstract
A study was conducted to determine the effect of the following factors on the concentration of active sulfhydryl (-SH) compounds in heated cream: (a) temperature of heating and length of exposure, (b) fat concentration, (c) separating temperature, (d) aeration, (e) length and temperature of storage, (f) metal contamination. The thiamin disulfide (TDS) method was used to measure the concentration of the -SH compounds. The cream was heated in a specially constructed tubular-heating apparatus in which heating time was controlled usually at 30 seconds. The greatest concentrations of active -SH compounds produced in 40% creams that were heated to 190[degree]F, 180[degree]F, and 170[degree]F were formed during periods of 5, 10, and 20 minutes, respectively. Maximum concentration was achieved by heating the cream to 190[degree]F for 5 minutes. When the rates of heating the cream to 190[degree]F were 15 seconds, 30 seconds, and 60 seconds, the quantities of active -SH compounds produced were directly and markedly increased. A direct relationship was noted between fat levels of cream and active -SH group production when creams of 20%, 30%, 40%, and 50% fat were flash-heated. Flash-heating to 190[degree]F produced in 50% cream 3 times the quantity of active -SH compounds as that produced in 20% cream, and twice that formed in 30% cream. However, as the exposure periods were extended to 5 minutes or more, the values became more nearly the same. The temperature of separation of milk was related inversely to concentration of heat-revealed -SH compounds in the resulting cream. Concentrations of active -SH compounds in 40% cream heated to 190[degree]F. for 5 minutes were equivalent to 22.7, 20.5, and 19.6 mg/l cysteine. HCl when the separation temperatures were 55[degree]F, 100[degree]F, and 135[degree]F, respectively. Vigorous aeration prior to high-temperature processing did not affect significantly the concentration of heat-activated -SH compounds nor the stability of the compounds during subsequent storage of the cream. About 60-70% of the heat-activated -SH compounds were retained in cream stored for 13 weeks at 5[degree]F, but only 10-20% were retained in cream stored 9 weeks at 40[degree]F. Addition of 1 ppm. Cu to cream before or after heating accelerated loss of active -SH compounds during storage at 5[degree]F, but the addition of Mn in the same concentration as the Cu was without effect. Oxidized flavor occurred in the copper-containing cream when the concentration of active -SH compounds had decreased to a level approximating 3 mg/l cysteine . HC1. The commercial significance of these findings is discussed.