Shelf-life improvement of distillers wet grains with solubles
It is known that the shelf-life of DWGS in the summer diminishes drastically compared to DWGS in the winter. This effect is primarily due to temperature, which drives mold growth in high moisture feedstocks. Therefore, the overall goal of this dissertation research was to increase the shelf-life of wet distillers grains by a factor of three from its current 3–4 days in warm summer conditions and 5–7 days in cold winter conditions. The first objective was to understand and quantify the effect of temperature (10, 20, and 25°C) and condensed distillers solubles (CDS) levels [0, 20, 30g/100g of Distillers Wet Grains (DWG)] on the shelf-life of DWGS under warm and cool aerobic storage conditions. Sample conditions which indicate shelf-life such as moisture, pH, fat acidity (FA), fungal growth and mycotoxin levels were measured in the DWGS samples before and after seven days of storage under three storage temperature levels (10, 20, and 25°C). We found that changes in temperature had the most significant effect on sample conditions (P<0.05). After seven days of storage, moisture content and water activity decreased with increase in temperature. We found fat acidity increased after seven days of storage and pH, fungal growth and mycotoxin levels increased with temperature. It was concluded that after seven days of storage at both warm and cool aerobic storage conditions, desired sensory, chemical, physical and microbiological characters were not retained. DWGS deteriorated less at 10°C than at 20°C and 25°C, likewise we saw less deterioration in 0 (g/100g) CDS than in 20 (g/100g) and 30 (g/100g) CDS. Additionally, deterioration and levels of three mycotoxins (aflatoxin, fumonisin and zearalenone) of DWGS stored under cool and warm conditions for a 7 day period were quantified. With the aforementioned knowledge, Objective 2 investigated in-package treatments of DWG using high voltage atmospheric cold plasma (HVACP) treatment in atmosphere modified with 65% CO2. The primary purpose was to increase product shelf-life by 3–4 fold. The treatments investigated were 1) in-package HVACP in an air gas blend, 2) CO2 modified atmosphere and 3) a combination of the two (1 and 2). Treated samples and controls were stored for 0, 7, 14, 21, and 28 days at 10°C and 25°C post-treatment, after which treated samples were measured for mold growth as indicated by pH, moisture and microbial load (CFU/g) in order to determine if shelf-life was extended. We found that treatments had a significant effect on shelf-life as indicated by CFU/g (P<0.003) and pH (P<0.0001). The combination treatment preserved the sample for 28 days with a 2.36 log (10°C) and 1.20 log (25°C) reduction in the microbial load, respectively, compared to the untreated samples. The in-package HVACP treatment alone resulted in a .34 and .59 log reduction after 28 days storage while CO2 treatment alone resulted in a 1.55 and .77 log reduction. The study showed the shelf-life of DWG (at 60-65% moisture) can be extended 3–4 fold for up to 28 days at 10°C and 21 days at 25°C by using a combined treatment of HVACP and CO2. In order to understand the efficacy of HVACP in reducing the microbial loads of DWG, the efficacy of HVACP in and out of the plasma field and the optimum treatment time (120s, 240s and 360s) were determined using the percentage of methylene blue discoloration and microbial loads (Log10 CFU). In Objective 3, the goal was to identify and evaluate critical parameters that increase the shelf-life of DWG. The critical parameters investigated were the gas composition, the effect of in-the-field and out-of-the-field sample exposure, sample bag size (volume), sample weight, treatment time, analysis delay time, and sample depth on HVACP efficacy. It was found that HVACP treatment did not affect product quality as indicated by chemical composition (protein, moisture, fat, fiber, ash and amino acid profiles). The results confirmed previous research on the inactivation of microbial species on DWG by HVACP treatments that increased shelf-life over an extended period of 28 days. However, variations in treatment time and package fill gas can have a significant effect on the microbial load reduction. This research is a first-step in understanding the efficacy of HVACP treatment of a wet granular feedstock and its potential for use in grain commodity. The results provide valuable data that can be used to design the scale-up of the HVACP generation system for commercial applications to wet feeds. In concluding, the research showed that HVACP treatment of DWG can lead to extended shelf-life, improved microbiological safety of the product and therefore reduce storage losses. (Abstract shortened by UMI.)
Ileleji, Purdue University.
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