Study On The Factors Affecting The Concentration Of IGF-I In Goat Milk

Goat milk contains not only numerous nutrients, but also a variety of bioactive substances with medical and health functioa 《Compendium of Materia Medica》 records that goat milk has a role in the treatment of diabetes, moreover, modern analysis shows that insulin-like growth factor I in goat milk has insulin effects due to both of their structure and function is similar to each other. Therefore, the objection of this paper mainly focus on systematical investigating factors which affect IGF-I concentrations in goat milk and lay a foundation for the development of functional goat milk products.This paper is mainly divided into five parts to research IGF-I concentrations in goat milk.In the first Part:effects of physiological factors on IGF-I concentrations in goat milk were studied, which mainly focus on effects of goat breed, lactation stage, lactation yield, lactation parity, milking interval on IGF-I concentrations in goat milk. The results showed that IGF-I concentrations in Guanzhong goat milk were the highest in all the goat breeds; in terms of lactation stage, colostrum of goat milk had higher IGF-I concentrations, especially in lambing first day which reached to 828.38ng·mL-1, while IGF-I concentrations range from 4.78 ng·mL-1 to 6.29 ng·mL-1 were relatively stable during its lactation period; in terms of lactation parity, the fourth parity of goat milk had the highest IGF-I concentrations; when it came to daily milk yield and milking interval, neither of them had significant effect on goat milk IGF-I concentrations.In the second part, effects of physiochemical conditions on IGF-I concentrations in goat milk were studied, which mainly focus on effects of temperature, pH, UV and metal ions on IGF-I concentrations in goat milk. The results showed that IGF-I concentrations in goat milk decreased when the temperature was higher than 80 ℃ and its concentrations will lose more during higher processing temperature; IGF-I concentrations in goat milk can be decreased by UV sterilization time and its concentrations sharply decreased after 15 min in ultraviolet irradiation. pH value had a significant effect on IGF-I concentrations in goat milk. IGF-I concentrations were rather stable at weak acid and neutral environment while had a lower concentrations when near the isoelectric point of 8.2 and alkaline environment; metal ions had effect on IGF-I concentrations in goat milk according to its type and concentrations. IGF-I concentrations were inhibited by Na+, Ca2+, Al3+, Zh2+, moreover, IGF-I concentrations were inhibited by low concentrations of Fe3+ and Cu2+ while activated by high concentrations of Fe3+ and Cu2+.In the third part, effects of crafts processing on IGF-I concentrations in goat milk were studied, which mainly focus on effects of pasteurization, UHT, stirring, homogenizing and fermentation on IGF-I concentrations in goat milk. The results showed that IGF-I concentrations were reduced by pasteurization while pasteurization concentrations of 72℃/15s had less effects on IGF-I concentrations in goat milk than others. UHT concentrations of 137℃/2s had bigger effects on IGF-I concentrations in goat milk. Neither stirring nor homogenizing had influence on IGF-I concentrations in goat milk. IGF-I concentrations would significantly decrease with fermentation.In the fourth Part, effects of IGF-I stability on digestive tract in goat milk were studied, which mainly focus on effects of IGF-I stability in artificial gastric juice, intestinal fluid, gastrointestinal fluid. The results showed that IGF-I concentrations and retentions in goat milk was relatively stable in first 2 h in its digestion period in gastric juice, intestinal juice and gastrointestinal fluids, while decreased rapidly when digestived over 2 h.In the fifth Part, effects of protection on IGF-I concentrations in goat milk were studied, which mainly focus on effects of sugars and salts on IGF-I protection in goat milk. The results showed that fructose, maltose, lactose and sucrose had better protection effects than glucose on IGF-I concentrations in goat milk; sodium citrate and phosphoric sodium had a similar protection effects on IGF-I concentrations in goat milk, too.