Influence of lactose concentration of milk and yogurt on growth rate of rats

Yogurt protects against growth retardation in weanling rats fed diets high in phytic acid

The purpose of this study was to determine the effects of adding yogurt to animal diets that were high in phytic acid (PA) and adequate in zinc (38 microg Zn/g). The PA:Zn molar ratio was 60:1. Zinc status was determined by documenting growth and measuring the zinc concentration in bone (tibia) and plasma. For 25 days, six groups (n=6) of Sprague-Dawley weanling rats were fed one of six AIN-76 diets. Half of the diets contained PA. Four of the diets contained yogurt with either active or heat-treated (inactive) cultures added at 25% of the diet. The diets were as follows: (a) AIN, (b) AIN with active yogurt, (c) AIN and inactive yogurt, (d) AIN with PA, (e) AIN with PA plus active yogurt and (f) AIN with PA plus inactive yogurt. Body weight, weight gain and zinc concentration in bone and plasma were measured, and food efficiency ratio was calculated. Rats fed diets with PA and yogurt had normal growth compared to the control group. Growth retardation was evident in the group fed the diet with PA and no yogurt. This group had significantly lower body weight compared to all other groups (P<.05). Rats fed diets with PA, with or without yogurt, had significantly lower zinc concentration in bone and plasma (P<.05). Adding yogurt to diets high in PA resulted in normal growth in weanling rats; however, zinc concentration in bone and plasma was still suboptimal.

Comparison of mineral and cholesterol composition of different commercial goat milk products manufactured in USA

Concentrations of 12 major and trace minerals and cholesterol in commercial goat fluid milk, evaporated, powdered, yogurt, and cheese products manufactured in the US were evaluated for compositional differences. Minerals were determined by an Inductively Coupled Argon Plasma Emission Spectroscopy (ICAP), while cholesterol was analyzed using colorimetric and gas chromatographic (GC) methods. Mean total solids content (%) of fluid milk, evaporated milk, powdered milk, yogurt, plain soft and Monterey Jack cheeses were: 11.3, 20.9, 94.1, 11.5, 32.5, and 57.7, respectively. Mean calcium and phosphorus contents (ppm, dry basis) of the corresponding products were: 103, 125; 440, 393; 7715, 7471; 161, 144; 691, 1105; 3492, 3067, respectively. The respective iron and zinc contents (ppm) of the corresponding products were: 0.062, 0.349; 1.518, 1.635; 3.33, 30.21, 0.117, 0.338; 7.16, 3.64; 8.86, 3.81. The levels of potassium (K) in cheeses were lowest among all the products including fluid goat milk, suggesting that a significant amount of K was lost during cheese manufacturing processes. Levels of all trace minerals were higher in yogurt and cheeses than in fluid milk. The levels of trace minerals in cheeses were greater than those in yogurt products. Iron and aluminum contents of certain goat milk products were considerably higher than normal, possibly due to contamination of minerals from manufacturing utensils and product metal cans. Sulphur contents of fermented products were significantly greater than those of fluid milk, which may be accountable for the microbial synthesis of sulfur containing proteins during the manufacturing processes of the products. Cholesterol contents (mg/100g, wet basis) of fluid, evaporated, powdered goat milk and Monterey Jack cheese determined by GC method were: 11.0, 24.9, 119.5 and 91.7, respectively. Cholesterol contents of the goat milk products analyzed by colorimetric method were substantially greater than those by GC method.

Lactic acid bacteria and human health

Although claims for health and nutritional benefits have been made for lactic acid bacteria in fermented dairy products for nearly a century, the nutritional and therapeutic value of these organisms is still controversial. This article will review the scientific basis of these claims. There are numerous studies showing fermentation of food with lactobacilli increase the quantity, availability, digestibility, and assimilability of nutrients. The basis for this conclusion comes from direct measurements of vitamin synthesis and from increased feed efficiency when fermented products are fed to animals. There have been a number of studies showing that various fermented dairy products lower serum cholesterol levels in humans and animals. These studies are reviewed and the validity of these findings are assessed. A summary of the evidence indicating that lactase deficient individuals can eat yogurt and the mechanisms involved in this toleration is reviewed. The role of fermented dairy products in inhibiting tumor growth and chemically induced tumors in animals is discussed and the possible mechanisms involved in this protective effect are reviewed. Fermented dairy products and lypholized lactobacilli preparations have been shown to be useful in treating and preventing various intestinal infections including; salmonellosis, shigellosis and antibiotic induced diarrhea. In this context a specific lactobacillus designated GG has been shown to be useful in treating recurring diarrhea caused by a toxin produced by Clostridium difficile.

Nutritional value of yogurt

Yogurt, made from fortified skim milk by conventional methods using Streptococcus thermophilus and Lactobacillus bulgaricus, was used in studies of the effect of fermentation on nutritional value of milk. In all experiments, the product was compared with the uninoculated base milk. The concentration of most vitamins was less in yogurt than in milk and was most noticeably so for biotin which was 60% less. The effect on folic acid content was inconsistent. In nutritional experiments with rats, high values for true digestibility, biological value and net protein utilization were obtained for both yogurt and its base milk, only minor differences being apparent between the two materials. In growth tests with rats, yogurt was not found to be consistently superior to the base milk when the milk was subjected to a double heat treatment to reduce bacterial contamination. Yogurt did not confer a nutritional advantage on fresh milk in this respect.