Abstract
Sustainable food packaging technologies that are environmentally friendly are needed by the food industry in response to the global call to reduce the global warming effect. The rapid growth of the South African pecan nut industry has seen the emergence of more value-added pecan nut-based products, which include roasted pecan nuts that are consumed as snacks or used as ingredients in formulating healthy foods. Given that current food packaging is made from synthetic plastic materials, the use of edible coatings as primary packaging for food could be one of the solutions to replace synthetic packaging materials. Therefore, the overall aim of this study was to investigate the potential application of Opuntia ficus-indica mucilage as a postharvest technique to preserve the quality, nutritional, and antioxidant properties of microwave-roasted pecan nuts.
In Chapter 3, optimum microwave roasting conditions for microwave power and time ranging from 96.45-803.55 W and 1.37-5.62 min, respectively, for pecan nuts to improve quality and nutritional properties were established using response surface methodology (RSM). Microwave power and roasting time significantly (p < 0.05) affected the total colour difference (TCD), 2.2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging capacity, and hardness. The study established that 700 W and 2.24 min were the optimum roasting conditions for the desired pecan nut quality attributes of TCD = 1863.391, hardness = 28.755 N, and DPPH radical scavenging activity = 33.877 mmol Trolox/g. Further, microwave roasting the pecan nuts at determined conditions did not significantly affect the essential fatty acids (cis-oleic, cis-linoleic, α-linolenic, and stearic acids), thus preserving the nutritional quality of the pecans. Limonene was the major volatile compound that provided microwave-roasted nuts with a citrus-like flavour. Other volatile compounds, which included alcohols, aldehydes, ketones, lactones, hydrocarbons, and carboxylic acids, were also identified. The results showed that microwave roasting may be optimised using RSM to produce pecan nuts with desired quality attributes and for various uses.
The study reported in Chapter 4 investigated the potential of a cactus mucilage (CM, 3%)-based edible coating enriched with ascorbic acid (AA) at various concentrations (0.03, 0.015, and 0.09%) in preserving the quality attributes of microwave-roasted (700 W, 2.27 min) pecan nuts at an accelerated temperature of 60 °C for 25 days. The study established that coating microwave-roasted pecan nuts with 3% CM enriched with AA at concentrations as low as 0.015% enhanced the colour properties, hardness, total phenolic content (TPC), total flavonoid content (TFC), ferric reducing antioxidant power (FRAP), and decreased the activities of peroxidase (POD) and polyphenol oxidase (PPO enzymes). Therefore, the study demonstrated that CM enriched with AA edible coatings has a huge potential to preserve the quality and prolong the shelf life of microwave-
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roasted pecan nuts during storage. These findings are desirable to the food industry, given their search for sustainable and environmentally friendly food packaging technologies.
Overall, the study has established the potential of RSM and AA enriched CM edible coating in optimising the microwaving roasting of pecan nuts and preserving their quality during prolonged storage. Therefore, this study provides scientifically based information that can be used to develop microwave roasted and cactus-mucilage coated pecan (Carya illinoinensis) nuts for improved quality, nutritional properties, and antioxidant activities, promote a food circular economy, and supports the achievement of United Nations Sustainable Development Goals (SDGs) focusing on nutrition, health, and environmental sustainability.