Complexes of lutein with bovine and caprine caseins and their impact on lutein chemical stability in emulsion systems: Effect of arabinogalactan.

Lutein is an important xanthophyll carotenoid with many benefits to human health. Factors affecting the application of lutein as a functional ingredient in low-fat dairy-like beverages (pH 6.0-7.0) are not well understood. The interactions of bovine and caprine caseins with hydrophobic lutein were studied using UV/visible spectroscopy as well as fluorescence. Our studies confirmed that the aqueous solubility of lutein is improved after binding with bovine and caprine caseins. The rates of lutein solubilization by the binding to bovine and caprine caseins were as follows: caprine αS1-II-casein 34%, caprine αS1-I-casein 10%, and bovine casein 7% at 100 µM lutein. Fluorescence of the protein was quenched on binding supporting complex formation. The fluorescence experiments showed that the binding involves tryptophan residues and some nonspecific interactions. Scatchard plots of lutein binding to the caseins demonstrated competitive binding between the caseins and their sites of interaction with lutein. Competition experiments suggest that caprine αS1-II casein will bind a larger number of lutein molecules with higher affinity than other caseins. The chemical stability of lutein was largely dependent on casein type and significant increases occurred in the chemical stability of lutein with the following pattern: caprine αS1-II-casein > caprine αS1-I-casein > bovine casein. Addition of arabinogalactan to lutein-enriched emulsions increases the chemical stability of lutein-casein complexes during storage under accelerated photo-oxidation conditions at 25°C. Therefore, caprine αS1-II-casein alone and in combination with arabinogalactan can have important applications in the beverage industry as carrier of this xanthophyll carotenoid (lutein).

Quantification of volatile compounds in goat milk Jack cheese using static headspace gas chromatography.

Goat milk Jack cheeses were manufactured with different levels of proteolytic endo- and exopeptidases from lysed bacterial cultures and aged for 30 wk. The aroma compounds that are potentially important in contributing the typical flavor of goat milk Jack cheese were quantified using static headspace gas chromatography. The concentrations of volatile compounds were evaluated every 6 wk throughout the aging period. Odor activity values of volatile compounds were calculated using the sensory threshold values reported in literature and their concentrations in Jack cheeses. Odor activity values of identified compounds were used to assess their potential contribution to the aroma of goat milk Jack cheeses. The odor activity values indicated that the ketones 2-hexanone, 2-heptanone, 2-nonanone, and 2,3-butanedione (diacetyl) were important odor-active compounds. The major odor-active acids found in this semi-hard goat milk cheese were butanoic, 2-methyl butanoic, pentanoic, hexanoic, and octanoic acids. Among the aldehydes, propanal and pentanal had high odor activity values and likely contributed to the aroma of this cheese. The concentrations of butanoic, pentanoic, hexanoic, heptanoic, octanoic, and nonanoic acids increased significantly in goat milk Jack cheese throughout aging. The extracted enzymes from lysed bacterial cultures that were added to the cheeses during manufacturing caused considerable increases in the concentrations of butanoic and hexanoic acids compared with the control. However, the lower concentration of peptidases resulted in an increased concentration of butanal, whereas more peptidases resulted in a lower concentration of 2-nonanone in goat milk Jack cheeses.

Size distribution of fat globules in goat milk.

Milk from French-Alpine goats and Holstein cows was obtained from a bulk tank immediately prior to analyses. Fat globule size was determined by laser particle size analysis. Individual globules of fat in goat milk ranged from 0.73 to 8.58 microm in diameter. The average diameter of particles based on volume to surface area ratio (dvs) was 2.76 microm and was less than the mean (dvs) of 3.51 microm for bovine milk, in which fat globules ranged from 0.92 to 15.75 microm in diameter. The specific surface area of particles in caprine milk was 21,778 cm2/ml, whereas the specific surface area of particles in bovine milk was 17,117 cm2/ml. Ninety percent of the total particles found in goat milk were less than 5.21 microm in diameter, whereas 90% of the total particles in bovine milk were less than 6.42 microm based on the volume frequency distribution. Dissociation of casein micelles by urea in goat whole and skim milk caused larger dvs values due to the effect of fat particles and reduced the specific surface area in both milks because the total number of detectable particles in both whole and skim milk was reduced.

Low molecular weight branched-chain and n-chain fatty acids in caprine and bovine colostrum.

Colostrum from French-Alpine and Anglo-Nubian goats and Holstein cows was collected and analyzed for both total and FFA of 12 and fewer carbon atoms. Short-chain VFA were separated from long-chain fatty acids using simultaneous distillation extraction. The n-butyl esters of fatty acids were quantified by gas chromatography, and their identity was confirmed by gas chromatography-mass spectrometry. The concentration of decanoic acid was 33 and 83% less in Holstein colostrum than in colostrum from Alpine and Nubian goats, respectively. Colostrum from Nubian goats had twice as much decanoic acid as colostrum from Alpine goats. The FFA in colostrum that differed between species but not between goat breeds were octanoic and decanoic acids. These respective fatty acids were approximately two and three times greater in colostrum from goats than in colostrum from Holsteins. The quantity of decanoic acid was different between goat breeds and between animal species. The ratio of total fatty acid concentration to free-state concentration for hexanoic acid appeared to be useful for differentiating between Nubian and Alpine goat colostrum as well as between Nubian and Holstein colostrums.

Inhibition of Growth of Staphylococcus aureus during Production of Acidophilus Yogurt. 1.

Inhibition of growth of a pathogenic strain of Staphylococcus aureus and production of a metabolite, thermostable deoxyribonuclease (TDNase), in acidophilus yogurt and yogurt were investigated. The causative factors of inhibition (lactic acid, hydrogen peroxide and bacteriocin) were assessed. Accumulation of hydrogen peroxide after 2 h of fermentation was 0.88 p-g/ml, which caused a significant difference in the population of S. aureus between yogurts with and without catalase. Growth of S. aureus in the acidified yogurt was reduced after 4 h of fermentation when the pH of the medium was 4.8 or lower. Significant differences were found for the S. aureus populations of the acidified treatment and acidophilus yogurt with catalase suggesting that inhibition was due to bacteriocin(s) produced during the yogurt fermentation. The TDNase was significantly lower in the acidified yogurt and was totally inhibited in the three cultured yogurts during the fermentation period.