Location: Dairy and Functional Foods Research
2021 Annual Report
Objectives
Objective 1: Characterize bioactive peptides released from dairy proteins by enzymatic digestion and investigate the effect of protein-carbohydrate interactions on the stability and bioavailability of these peptides in dairy foods. [NP306, C1, PS1C]
Sub-objective 1.A: Production and characterization of bioactive peptides from dairy proteins through enzymatic digestion.
Sub-objective 1.B: Develop encapsulation-based delivery systems to protect and enhance the bioactivity and effectiveness of these peptides.
Objective 2: Identify novel bioactive prebiotic oligosaccharides from plant (fruit and vegetable) and animal (milk) sources in food processing low-value by-products. [NP306, C1, PS1B]
Approach
New bioactive compounds will be developed from dairy proteins, oligosaccharides and plant dietary fiber. Bioactive compounds will include antioxidative peptides from milk and dairy products. We will identify these bioactive peptides released through the enzymatic digestion of dairy proteins and products, and investigate the effect of milk fatty acids and oligosaccharides on the production of these peptides. Novel prebiotics will be characterized and compared with galacto-oligosaccharides derived from lactose and milk oligosaccharides. Pectic oligosaccharide prebiotic activity will be evaluated using animal models, mixed culture fecal fermentation and determining their effects as human bioactive food ingredients. We will develop synbiotics in live microbial systems such as yogurt and with tea products. Oligosaccharide anti-adhesive activity against pathogens will be determined with tissue culture cells. We will determine dietary fiber characteristics in fruit and vegetable processing byproducts.
Progress Report
Objective 1: With its complete essential amino acid profile, whey protein has been used in various food products and investigated as potential edible food packaging materials. Previous research demonstrated that composite films could be made from biofiber gum (BFG), a low-value by-product of the corn wet or dry milling process of biofuel industries and chitosan (CHI). However, these films exhibited high water solubility, gas permeability, and low mechanical strength, limiting their applications for high moisture foods. To improve the properties of the films, we created conjugates between whey protein isolate (WPI) and BFG (WPI:BFG) through a Maillard-type reaction. We then used these conjugates to develop films and coatings using carvacrol as the antimicrobial agent in the formulations. We evaluated the antimicrobial efficacies of the films against E. coli, Salmonella, Listeria, spoilage fungi, and bacteria using both in vitro and in vivo tests. We demonstrated that both the conjugate and composite films effectively reduced the populations of E. coli, Listeria, and native microorganisms on tomatoes and fresh-cut apples stored at 4 degrees C for up to 7 and 21 days, respectively, as well as decreasing the populations of Salmonella and bread fungi in growth media. However, the WPI:BFG conjugate films maintained their antifungal properties for a more extended period of time than the BFG+CHI composite films. The results also indicated that WPI:BFG conjugate films had lower water solubility, reduced oxygen and carbon dioxide permeability, and higher mechanical strength than the BFG+CHI composite films. This work showed that the films and coatings developed can be used directly on the food surface or as films to modulate the headspace. This research effort could meet the increasing demands for natural, biodegradable, and environment-friendly packaging materials and safe and effective antimicrobial agents suitable for various foods.
Objective 2: Blueberry is a well-known source of antioxidants and prebiotic dietary fiber. Detailed composition and structure of blueberry pomace (PF) remaining after commercial blueberry fruit puree processing, as well as the water-soluble and water-insoluble fractions, were determined. The PF was comprised of dietary fiber (60.8%) that was largely insoluble (46.2% vs. 14.6% soluble dietary fiber), pectin, xyloglucan, arabinoxylan, and mannan polysaccharides, fructose (11.22%), and glucose (10.37%) free sugars, protein (9%), fat (5%), and anthocyanins (6444.5 µg/g). The most abundant anthocyanins detected in PF were malvidin 3-arabinoside, and peonidin 3-glucoside, and the pectin was determined to be methyl-esterified and acetylated rhamnogalacturonan I with a 4,5-unsaturated function at the non-reducing end based on oligosaccharide structural analysis. Blueberry PF xyloglucan oligosaccharide side chain structures included xylose, arabinose, and galactose consistent with arabino-xyloglucan structure. Microwave-assisted extraction of blueberry PF (pH 2 for 10 min at 80 degrees C) was performed to more clearly elucidate pectin structure and revealed a pectin polymer with high molar mass (1072 kDa) viscosity that was dependent upon the molar mass. A random coil shape was confirmed for both the blueberry PF and microwave extracted blueberry pectin, agreeing with previous reports that flexible blueberry pectin contributes to strong anthocyanin binding. The blueberry pomace anthocyanin content was slightly higher than that reported for fresh whole blueberry fruit, which suggests that most blueberry anthocyanins adhered to the pomace fiber and most likely the insoluble pectin, during and after processing.
Accomplishments
1. Bioactive blueberry fiber. Blueberries are health-beneficial due to their antioxidants and dietary fiber, but what happens to these compounds during fruit processing? ARS researchers at Wyndmoor, Pennsylvania, determined the composition of blueberry fiber remaining after blueberry fruit puree processing by a major food ingredient company. The insoluble blueberry fiber contained health-beneficial carbohydrates that bound bioactive antioxidants during blueberry processing, making the puree a very healthy food ingredient.
Review Publications
Hotchkiss, A.T., Chau, H.K., Strahan, G.D., Nunez, A., Simon, S., White, A.K., Yadav, M.P., Dieng, S., Hirsch, J. 2020. Blueberry fiber pectin, xyloglucan and anthocyanin structure and function. Food Hydrocolloids. https://doi.org/10.1016/j.foodhyd.2020.106572.
Qi, P.X., Chau, H.K., Hotchkiss, A.T. 2020. Molecular characterization of the interacting and reacting systems formed by alpha-lactalbumin and sugar beet pectin. Food Hydrocolloids. 1-14. https://doi.org/10.1016/j.foodhyd.2020.106490.
