Recovery of functional ingredients from sweet corn (Zea mays) cobs

Sweet corn cob (SCC) is an agricultural lignocellulosic waste generated from the corn processing industry and is available in large amounts. However, the production of high value-added products from SCC is limited, most of it is either discarded or used for the production of biomasses. Hence, research into the comprehensive utilization of SCC as a functional food is of great interest. As such, the aims of the current research were (i) to identify and characterise the functional compounds in SCC, (ii) to examine the effectiveness of enzymatic hydrolysis in the release of ferulic acid (FA) from SCC, (iii) to evaluate the effect of phenolic compounds from SCC on gut microbiota and (iv) to investigate the effect of the incorporation of SCC flour in the baking of rice flour muffin. Compositional analysis of SCC (Chapter 2) showed that SCC is comprised mainly of cellulose and hemicellulose. In addition, elemental analysis showed that phosphorus, potassium and magnesium are present in SCC at a higher concentration compared to the rest of the minerals being tested. Alkali hydrolysis of the free, esterified and insoluble-bound fractions of SCC showed that the insoluble-bound fraction had the highest amount of total phenolic content, antioxidant capacity assays (TEAC, DPPH and FRAP) and contained the highest amount of FA and p-coumaric acid (pCA). More than 80% of the FA and pCA was present in SCC as insoluble-bound form. Supercritical fluid extraction of carotenoid compounds showed that SCC contained the highest amount of β-carotene, followed by zeaxanthin and lutein. Results showed that SCC could be a source of natural colorant, antioxidants and functional ingredients. Raising concerns over the environmental impact due to the usage of large amounts of chemical solvents has increased the interest of using enzymatic hydrolysis, a more green and sustainable approach in the extraction of bound phenolic compounds, as compared to conventional solvent extraction. Response surface methodology (Chapter 3) showed that under optimized conditions, the combination of enzymes ferulic acid esterase (FAE) and xylanase (XY) released half the amount of FA, as compared to alkali hydrolysis. Therefore, novel technologies can be further explore to increase the efficiency of enzymatic extraction of FA from SCC. The therapeutic effect of phenolic compounds depends on their bioactivity, where it is modulated by the gut microbiota depending on their bioavailability. The effect of SCC (high in fibre and bound phenolic acid content) on the gut microbiota ecology, was used to compare against the SCC extract (contains free phenolic acids and xylooligosacchrides) using batch culture fermentation (Chapter 4). SCC extract showed a potential bifidogenic effect by showing a trend of an increase in Bifidobacterium and a decrease in pathogenic Clostridium perfringen, although the results were not significant. Furthermore, the SCC which is high in fibre content, showed an increase in the production of beneficial short chain fatty acids (SCFA), a key source for the intestinal epithelium and liver. Incorporation of SCC flour in the baking of rice flour muffin showed improvements in the texture and total ferulic acid content of baked muffin, as compared to control muffin baked with 100% rice flour (Chapter 5). Muffin incorporated with ≤ 20% of SCC flour showed a softer crumb and improvements in terms of height, colour and nutritional value coupled with an increase in fibre and ferulic acid content. Overall, SCC can be a functional food as it can be a source of fibre, phosphorus, potassium, phenolic (ferulic and p-coumaric acid) and carotenoid compounds. Enzymatic hydrolysis can be used as an alternative method in the release of the ferulic acid from SCC. In addition, SCC significantly increased the production of beneficial SCFA during colonic fermentation. Furthermore, SCC can be used as an alternative flour in baking to improve the texture and quality of gluten-free rice muffin.