The technological and nutritional challenges of producing gluten-free pasta from cassava and banana flours : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

Pasta is a common cereal product made from wheat, and has affects the health of gluten intolerant people. A gluten-free diet is a must for coeliac patients and has recently become an option for a healthy lifestyle. Gluten-free materials have also become alternative sources in food products development in the wider food industry to counter the dependence on imported wheat. Some of the potential alternative base materials are banana and cassava flour due to their wide availability and physicochemical characteristics (Kumar, Saravanan, Sheeba, and Uma, 2019; Odey and Lee, 2020). However, there remains a challenge in developing good quality food products based on gluten-free materials since the absence of gluten can lead to technological limitations in forming good quality of food structures. The effort to improve the quality of cereal food products, alongside a healthy lifestyle choice, can be achieved by adding natural protein resources into the gluten-free flour mixture. Egg white protein has been proven to enhance gluten-free cereal products quality, as too has soy protein isolate, used as a vegetable protein source (Gao et al., 2018). This study evaluated two different types of gluten-free flours, banana flour and cassava flour, that were combined in various formulations (0 to 100% proportion at 25% intervals) were used to produce pasta. Subsequently two different protein additions (soy protein isolate and egg white protein) at different levels (0, 5, 10 and 15%) were used to stabilise pasta quality. The chemical, physical, textural, digestibility properties, nutritional, and sensory characteristics of the raw materials and cooked pasta were determined and compared to semolina pasta as a control. The research aimed to investigate the utilisation of alternative base materials (cassava and banana) and a technical additive (protein for gluten functionality and fortification) on the physical and nutritional quality of gluten-free pasta. The assessment of the raw materials showed that banana and cassava flour had a lower protein content (4.54 and 1.41%) than semolina flour, however the amylopectin content and total dietary fibre contents were higher in banana and cassava flour (16.46 and 10.99%) compared to semolina flour (12.36 and 7.07%, respectively). Banana flour exhibited the highest resistant starch, total phenolic content (TPC), and antioxidant capacities, while cassava flour had the lowest values for these characteristics. The amino acid evaluation showed banana and cassava flour had a better ratio of total essential amino acid and total amino acid (35.37 and 29.95% versus 23.34%) but had lower limiting essential amino acid values (0.98 and 1.51% versus 11.12%) than semolina flour. Gluten-free pasta producing from banana-cassava flour combinations resulted in higher dietary fibre content, lower protein content, and a darker colour compared to the semolina pasta control. All gluten-free pasta had lower optimum cooking time (2.8-4.2 min) and water absorption index (23.28-86.81%), but higher cooking loss (15.18-28.75%) than the control. Gluten-free pasta made from 75:25 banana : cassava flours and 100% banana flour had the best pasta-quality and the lowest reduced predictive glycaemic loading among other gluten-free pasta formulations. These formulations were selected for the following stage of this study. The addition of soy protein isolate/egg white protein showed significant differences in physicochemical properties compared to semolina pasta, and gluten-free pasta with no protein enrichment. The level of protein addition increased the protein content of all gluten-free pasta formulations. Soy protein isolate addition gave higher protein content than egg white protein. There were no significant effects of both protein addition to either insoluble or soluble dietary fibre content. The protein fortification reduced a resistant starch content due to a lower portion of total starch in the gluten-free pasta composition. Cooking properties of pasta (optimum cooking time, swelling index, water absorption index, and cooking loss), and texture properties (firmness and extensibility), were affected by the level and the type of protein addition. Gluten-free pasta made from 75:25 banana : cassava flours showed similar trend to the gluten-free pasta made from 100% banana flour in physico-chemical, cooking properties and texture properties. Egg white protein and soy protein isolate addition, and different gluten-free flour formulations, exhibited different effects on the nutritional and digestibility of gluten-free pasta. The addition of both proteins decreased starch digestibility, increased protein digestibility, improved amino acid profile, and protein digestibility-corrected amino acid score whereas only soy protein isolate enhanced the TPC and antioxidant capacity of the gluten-free pasta. A 25% cassava flour inclusion into gluten-free pasta formulation reduced the TPC and antioxidant capacities of the pasta. Gluten-free banana-cassava pasta with added egg white powder had better customer acceptance and purchase intent compared to soy protein isolate inclusion. To sum up, banana and cassava flours could be utilised in gluten-free pasta production with high fibre content and low starch digestibility properties. Soy protein isolate and egg white protein could be incorporated into gluten-free pasta based on banana and cassava flours to promote pasta quality and nutritional properties of alternative functional products. Gluten-free pasta made of 75% banana flour and 25% cassava flour with 5% egg white protein performed the best gluten-free pasta quality, nutritional properties and moderate sensory acceptance.