Njume, Collise (2020) Bioactive Components of Australian Native Plant species and their Potential Antidiabetic Application within the Indigenous Community. PhD thesis, Victoria University.

Abstract

Type 2 diabetes mellitus (T2DM), driven by overweight and obesity linked to unhealthy diets, is the fastest-growing non-communicable disease in Australia. Considering that food is an important parameter in the regulation of blood glucose response, replacing ‘junk food’ with products that are good regulators of postprandial blood glucose (PPG) may go a long way to reduce the rate of T2DM in Australia. This study was designed to develop new food products that have the potential for use as nutritional preventatives against escalating levels of T2DM within the Australian Indigenous community. Edible portions of eight Australian native plant species namely; Leucopogon parviflorus, Arthropodium strictum, Carpobrotus rossii, Rhagodia candolleana, Typha orientalis, Correa alba, Dianella revoluta and Acacia longifolia were collected from the coast of Warrnambool, Victoria Australia. The plant species were analysed for proximate, minerals, fatty acids and phenolic composition following the methods of the Association of Official Analytical Chemistry (AOAC), Inductively Coupled Plasma Spectometry (ICP), High performance liquid chromatography (HPLC) and gas chromatography/Mass spectrometry analysis (GCMS). Plant species that exhibited significantly high amounts of nutrients, antioxidants and antidiabetic polyphenols were selected for development of potential antidiabetic food preventatives. The developed food products (Acabungi flakes and crackers) were evaluated for acceptability and the cracker was further studied for stability and microbiological load. Its Glycaemic index (GI) was estimated by in-vitro enzymatic starch hydrolysis. All eight plant species were found to be sources of carbohydrates (39.7 - 65.5%), proteins (2.6 - 15.1%), fats (1 - 14.3%), total dietary fibre (1.5 - 17.2%) and contained Ca, Mg, Na and K. The species exhibited consistent antioxidant activity with phyto-components of gallic acid (GA), epigallocatechin (EPC), catechin (CH), epigallocatechingallate (EPG), dihydroquinidine (DHQ), ρ-coumaric acid (PCA) and luteolin (LT). The betacyanin, betanidin 5-O-β-glucoside (BT) was detected in R. candolleana (700 mg/kg) and C. rossi (244 mg/kg) while the alkaloid, Dihydroquinidine (DHQ) was detected in D. revoluta (101 ± 5.7 mg/kg) and T. orientalis (17 ± 7.1 mg/kg). However, not all the compounds were isolated from a single plant species and except for BT, higher quantities of components were extractable in methanol than water (P<0.05). Palmitic, oleic and linoleic acids were the dominant of 10 fatty acids detected in the native species with record quantities of 4.2 - 39%, 12.3 - 39% and <0.5 - 44% respectively. No single species had all 10 fatty acids. The cracker, with a record overall consumer acceptability of 70.5% remained stable and unchanged with no microbial growth after 35-days storage at room temperature under light and in the dark. The cracker contained significant amounts of total dietary fiber, proteins, complex carbohydrates and exhibited a low GI of 47.7. R. candolleana and A. longifolia were found to have high contents of betanin and linoleic acid respectively, two components with potentially wide industrial application. Further studies to determine the antidiabetic mechanism of action of the cracker would shed more light on its potential application.

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