Evaluation of Heat Treatment on the Microbiological and Nutritional Properties of Supermarket-Derived Food Waste as a Potential Substrate for Insect Rearing

Sivabalan, Mathumita (2025) Evaluation of Heat Treatment on the Microbiological and Nutritional Properties of Supermarket-Derived Food Waste as a Potential Substrate for Insect Rearing. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

The increasing global food waste issue particularly from supermarket sources, is a critical environmental and economic concern. One of the solutions is the recycling of supermarket-derived food waste (SFW) as a substrate for black soldier fly larvae (BSFL) rearing, which is in line with circular bioeconomy goals. However, microbiological safety concerns, particularly contamination with pathogens like Salmonella spp., Staphylococcus aureus, total viable count, and Enterobacteriaceae, necessitate effective pre-treatment. Moreover, if a heating step is not well optimized for the intended use, it could result in overprocessing and nutritional loss as well as additional expenses. The objective of this research was to assess the effects of applying heat treatment at 60 degrees Celsius for 10, 20, and 30 minutes on the microbiological and nutritional properties of SFW and to identify the best treatment time that ensures microbiological safety with minimal loss of nutrients. The procedure involved SFW homogenate preparation and exposure to controlled heat exposures. Microbiological analysis focused on total viable count, Salmonella spp., Staphylococcus aureus, and Enterobacteriaceae, while nutritional analysis was assessed using the iodine and biuret tests to determine the presence of carbohydrates and proteins respectively. Results showed that all heat treatments eliminated Salmonella spp and Staphylococcus aureus completely, and significantly reduced total viable count and Enterobacteriaceae levels. For Staphylococcus aureus, Total Viable Count (TVC), and Enterobacteriaceae, the one-way ANOVA results (p < 0.001) verify that the observed decreases in microbial counts throughout various treatment durations are statistically significant and not the result of chance. Since the ANOVA results indicated statistical significance, a post-hoc Tukey's HSD test was conducted to identify which specific treatment groups showed significant differences. For Staphylococcus aureus, the test revealed that the "Before Heat Treatment" group (4.1 ± 0.2) was significantly different from the 10-minute (2.0 ± 0.1), 20-minute, and 30-minute treatment groups (both <1.0). In the case of Total Viable Count (TVC), Tukey's HSD showed that all treatment groups differed significantly, with each longer heat treatment duration leading to a notable reduction in TVC levels. Likewise, for Enterobacteriaceae, the test identified significant differences among all groups, with the 30-minute treatment group (<1.0) showing a markedly lower count compared to all other groups, including the initial count (5.30 ± 0.3). Nutritionally, there was gradual breakdown of proteins and starch with increasing heat treatment. The optimum result was achieved at 60 °C for 10 minutes, which completely inactivated the pathogens without loss of detectable quantities of carbohydrates and proteins. This heat treatment time is therefore optimal to ensure microbiological safety without excessive loss of nutrients. The findings show that treated supermarket food waste can serve as a safe and nutritionally suitable substrate for insect rearing. Future studies should seek to assess the impact of such treated substrates on BSFL growth performance and explore non-thermal treatments that can further enhance nutrient retention and effectiveness of bioconversion processes. Keywords: Food waste; Black soldier fly larvae; Heat treatment; Microbiological safety; Nutritional properties.