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Has files: YesSubject: search.filters.subject.Gluten-free foods

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    Enzymatic modification of amadumbe flour for gluten-free applications
    (2018) Manhivi, Vimbainashe Edina; Kudanga, Tukayi; Amonsou, Eric Oscar
    The production of gluten-free bread from gluten-free flours remains a technological challenge. Different strategies have been employed to improve the dough rheological properties. Enzymatic modification of the proteins in dough may result in polymers that mimic gluten. In this study gluten-free amadumbe flour was modified using single and optimised multiple crosslinking enzyme systems for the improvement of rheological properties and bread quality. Specifically, compositional, rheological and thermal properties of amadumbe and cactus mucilages were investigated as potential hydrocolloids and as substrates for crosslinking enzymes in gluten-free bread production. The effects of laccase, tyrosinase and transglutaminase on amadumbe dough rheology were also investigated. Model reactions were used to demonstrate the different enzymatic reactions occurring in amadumbe dough treated with the crosslinking enzymes. The combination of enzymes was then optimised using response surface methodology (RSM), to produce dough with improved G’ and G”. Xanthan gum, amadumbe mucilage or cactus mucilage were then added to the dough with an optimum enzyme combination. The effect of these enzymes and hydrocolloids were studied on the bread properties. The mucilages had a similar composition of monosaccharides and amino acids, except for the absence of rhamnose in amadumbe mucilage. Cactus mucilage showed a pseudoplastic flow behaviour whilst amadumbe mucilage showed a Newtonian flow behaviour at up to 5% (w/v) concentrations. The mucilages contained phenolics and amino acids such as lysine, tyrosine and glutamine, which are potential enzyme substrates. Trametes versicolor laccase catalysed the crosslinking of phenolics and thiols producing a wide range of crosslinking products which included homo- and hetero-conjugates, as demonstrated by mass spectroscopy. Thiol and total phenolic contents of dough decreased by up to 28% and 93%, respectively, as laccase activity was increased (0-3 U/g flour), confirming crosslinking reactions. Laccase-catalysed modification of amadumbe dough increased dough viscoelasticity, as shown by the increase in G’ and G”. Tan δ decreased with increase in laccase activity indicating an increase in the elastic character of the dough. Tyrosinase oxidation resulted in a 7.7 – 39.4% decrease in dough free amine and a 16.8 – 46.3% decrease in the dough thiol content as activity was increased (0-80 U/g flour). Transglutaminase treatment decreased the dough free amino groups by 10 – 38.1% as activity was increased from 0 to 2 U/g flour. An increase in dough G’ and G”, showed that both transglutaminase and tyrosinase improved dough viscoelasticity. Evidence of transglutaminase and tyrosinase crosslinking was provided by relevant model reactions monitored by mass spectrometry. Reaction model data showed the formation of the glutamyl-lysine bond due to transglutaminase crosslinking, whilst tyrosinase crosslinking resulted in disulphide and dityrosine bond formation. The viscosity and elasticity of amadumbe dough containing soy protein were optimised using a central composite design and the enzyme combination resulting in maximum G’ and G”, and minimum Tan δ was selected and verified. The predicted optimal enzyme activities (LAC, 1.78 U/g flour), (TYR, 79 U/g flour) and TG, 1.97 U/g flour) resulted in amadumbe dough that had a higher G’ and G”, as well as bread with a higher specific volume and lower crumb hardness compared to the dough without enzymes or with a single enzyme system. Addition of cactus and or amadumbe mucilage to the dough containing the optimum enzyme combination further improved dough viscoelasticity, improved bread specific volume, and significantly (p < 0.05) reduced bake loss and crumb moisture loss. The better bread was produced from dough with an optimum enzyme combination and 2% cactus mucilage. Sensory evaluation revealed that enzymes and cactus mucilage improved bread texture, appearance and overall acceptability but did not significantly affect bread aroma and taste. Overall, the combined effect of multiple enzyme-catalysed modification of gluten-free amadumbe flour and amendment with hydrocolloid resulted in more acceptable bread quality than single enzyme systems or unmodified flour. Therefore the optimised combination of enzymes have potential for application in gluten-free bread production.
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    The effects of laccase and xanthan gum on the quality of glutten-free amadumbe bread
    (2018) Seke, Faith; Kudanga, Tukayi; Amonsou, Eric Oscar
    Celiac disease (CD) is an auto-immune disorder that is triggered by the consumption of gluten in predisposed individuals. The only remedy that has been proposed thus far is total exclusion of gluten from the diet. This may be the most difficult task to most celiac disease patients for most of the convenient and widely consumed baked products such as bread are prepared using ingredients that contain gluten. The replacement of gluten in the baking industry comes with some implications on the overall quality of the baked products, especially bread. It has been observed that gluten-free baked products currently on the market are of poor texture, less volume, not visually appealing and have a bad taste. Hence, the need for polymeric substances that can mimic gluten properties, yielding baked products with similar characteristics as the gluten-containing counterparts. Various crops such as rice, sorghum, sweet potato and cassava have been used and additives such as hydrocolloids, protein-based ingredients, emulsifiers and enzymes included to improve gluten-free bread quality. The use of carbohydrate-rich tubers and protein-rich legumes as gluten-free ingredients shows great potential in the food industry. Amadumbe (Colocasia esculenta) is a carbohydrate rich tuber which is highly underutilized in South Africa and contains vast amounts of mucilage, a hydrocolloid which can be of great help to improve dough rheology. Hydrocolloids have been reported in literature to have the ability of improving dough water holding capacity and improving dough viscosity hence facilitating gas retention and impacting on the overall quality of the baked product. However, despite the presence of mucilage, amadumbe is very low in protein and it is difficult to produce bread with properties that resemble gluten-containing bread. Hence the need for protein supplementation which may also potentially facilitate protein cross-linking during bread making. Legume proteins from crops such as soy bean and bambara groundnuts contain abundant quantities of lysine, tyrosine and cysteine which could potentially be manipulated through the use of enzymes such as laccase in order to initiate the formation of a network similar to gluten. The project investigated the effect of laccase and xanthan gum (a hydrocolloid) on the quality of gluten-free bread supplemented with bambara groundnut flour and soy protein isolate as protein sources. Flour blends were prepared using a ratio of 70:30 (amadumbe flour: bambara groundnut flour) and 88:12 (amadumbe flour: soy protein isolate) based on a targeted protein content of 16 g/100 g and the quality properties were determined. Colour analysis showed that amadumbe flour had a higher L* value compared to the other flours and the blends, showing that amadumbe can be used in applications where food colour contributes to food perceptions. However, when bambara groundnut flour and soy protein isolate were added the L* value decreased. The nutritional profile of the individual flours and the blends showed that amadumbe flour protein content was improved with the addition of bambara groundnut flour and soy protein isolate in the above-mentioned ratios. The protein content of amadumbe increased from 2.36 g/100 g to 15.87 g when bambara groundnut flour was added and to 16.10 g/100 g when soy protein isolate was added, values that were close to the targeted protein content. Incorporating bambara groundnut flour and soy protein isolate in amadumbe flour resulted in improved water absorption capacity, foam capacity and stability as well as emulsion capacity and stability of the amadumbe flour. However, there was no significant difference in oil absorption capacity between amadumbe flour and the blends. The blends were then used to formulate different bread samples incorporating the enzyme laccase (25 nkat/g flour) and a hydrocolloid, xanthan gum (1%). Laccase-mediated treatment of gluten-free amadumbe dough resulted in a 30% decrease in the free sulfhydryl groups and a 40% decrease in phenolic content indicating that crosslinking had occurred. Laccase action resulted in a 64% increase in bread specific volume and a 32% decrease in bread crumb hardness. Sensory analysis showed that laccase-treated bread samples were more acceptable compared to the non-treated bread samples in terms of appearance, texture, aroma and taste. The acceptability index varied between 46% and 86.2%. This study showed that there is great potential of laccase in gluten-free bread making. The addition of 1% xanthan gum to amadumbe dough supplemented with bambara groundnut flour and soy protein isolate resulted in gluten-free amadumbe bread with improved crumb texture and specific volume, and decreased the rate of moisture loss. Sensory analysis also revealed that gluten-free amadumbe bread with added xanthan gum was more acceptable compared to the bread samples without xanthan gum. The acceptability index of the bread samples ranged between 40% and 85%. The resulting bread with xanthan gum showed that hydrocolloids such as xanthan gum can be successfully used in the development of gluten-free baked products. Overall, this study has shown that the incorporation of laccase and xanthan gum to gluten-free amadumbe bread results in bread with improved and acceptable bread properties.