Nutrient profile, functional properties, and microstructure of dried waste milk products for use as a potential animal feed
A study was conducted to determine the feasibility of concentrating the wastewater of a butter/powder factory for use as an animal feed. Two concentrated products were evaluated: recovered milk product (RMP), which is the direct factory waste stream; and formulated recovered milk product (FRMP), which is a product made by combining RMP and separator de-sludge in a 3:1 ratio. Three pilot scale dryer systems were used to concentrate the product: a spray dryer, a roller dryer, and a pulse combustion dryer. Dried samples were analyzed for fat, moisture, protein, ash, nitrates, chloride, pH, calcium, phosphorus, sodium and amino acids. Values for total digestible nutrients, nitrogen free extract and lactose were calculated. Functional properties were measured by free-fat, insolubility index, wettability, and particle size distribution. Additionally, the microstructure was examined using environmental scanning electron microscopy (ESEM). The objectives to this study were to: 1) further concentrate and dry RMP into a powder to reduce hauling cost, improve consistency, and increase the storage life of the product; 2) add other by-products to the RMP to improve the nutrient profile; and 3) compare three drying systems as to the effect to the nutrient profile, functional properties, and microstructure of the dried product. The protein content in the FRMP was significantly (P<0.05) higher than in the RMP. The nitrate (NO3) concentration in the RMP was significantly (P<0.05) higher than the NO3 concentration in the FRMP. The Mojonnier fat determination test resulted in higher fat content for the products dried on the spray and pulse dryer compared to the Soxhlet fat determination method. The roller drier produced a powder that was significantly (P<0.05) higher in free-fat compared to the other two drier systems. The pulse combustion dryer produced the most soluble product as determined by the insolubility index. The available lysine concentration in the product dried on the roller dryer was significantly (P<0.05) lower than the available lysine concentrations in the product dried on the spray and pulse combustion dryers. The microstructure of the powders was different for each of the dryers when examined using ESEM.
roller dryer, pulse combustion dryer, spray dryer
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