MICROWAVE-ASSISTED BLANCHING EFFECTS ON THE FRYING QUALITY OF SWEET POTATO: ANN MODELLING OF FRYING KINETICS

AYOOLA, AYOOLUWA SAMUEL (2021) MICROWAVE-ASSISTED BLANCHING EFFECTS ON THE FRYING QUALITY OF SWEET POTATO: ANN MODELLING OF FRYING KINETICS. Masters thesis, Landmark University, Omu Aran, Kwara State.

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Abstract

Deep frying of Sweet potato chips is often associated with high oil uptake which raises so many health concerns. Several pre-treatment methods have been found to decrease oil uptake. This study evaluated the effects of microwave-assisted blanching techniques on the frying kinetics and quality characteristics of sweet potato chips. Also, the frying kinetics were modelled with both mathematical models and artificial neural networks (ANN). Microwave blanching (MW), hot water + microwave blanching (HWMW) and osmotic dehydration + microwave blanching (OSMW) pre-treatments of potato chips were done while untreated samples were used as control (CT). The frying temperatures were at 130,150 and 170°C for 2, 4, 6, 8 and 10 minutes. The moisture ratio (MR) was fitted to 11 empirical models and the oil uptake was fitted to 5 empirical models. The model performance was also compared with ANN modelling. The results showed that ANN performed better in fitting the moisture ratio and oil uptake with R2 = 0.9, RMSE= 1.034 and SSE= 0.131301864 while the Middili model had the best fit with R2 = 1, RMSE= 0.002559 and SSE= 0.00001309 among the mathematical models used. HWMW pre-treated samples had the lowest moisture ratio of 0.376 (10 minutes of frying), while OSMW had the lowest oil uptake of 1.9% (8 minutes of frying) at temperatures of 170°C and 130°C respectively. At 150°C and 170°C, all pre-treated samples had higher k values than the untreated sample. Effective moisture diffusivity ranged from 1.212 ×10−6 to 9.999 × 10−7 m2/s and highest activation energy of 117.14KJ/mol was found at OSMW. Oil uptake of the control sample ranged from 5.4% to 69.2% all through this study. This was significantly reduced as a result of the pretreatment methods adopted. MW, HWMW and OSMW pre-treated sweet potato chips had oil uptake from 5.2% to 37.4%, 6.4% to 39.4% and 1.9% to 52.6% respectively. Statistical analysis showed that microwave-assisted blanching pre-treatments had significant effects (p<0.05) on the quality characteristics (colour, texture, ascorbic acid, microstructure, electrolyte leakage, shrinkage) of the fried sweet potatoes. Samples pretreated with osmotic dehydration combined with microwave-assisted blanching had higher significant effects on quality characteristics compared to other pre-treated and untreated samples. OSMW (170°C) sample had the highest hardness value (13.841g/mm). The study also showed that the electrical conductivity of the fried samples at all frying conditions increased with increase in frying temperature, the OSMW (170°C) had the highest electrical conductivity of 200.67 µs/cm while CT (170°C) had the lowest electrical conductivity 159 µs/cm. Microwave-assisted blanching pre-treatments had significant effects on the ascorbic acid value retention while CT had the least retention. Bulk density of fried samples also ranged from 0.44 to 0.53g/cm3. Microstructure analysis revealed that the untreated samples had the highest oil retention in comparison with the pre-treated samples. Furthermore, the colour difference values of the samples also increased as the frying temperature increased. OSMW (170°C) sample had the highest colour difference of 49.49 while the control sample had the lowest colour difference of 33.46. Shrinkage values for the deepfried sweet potatoes ranged from 5.7mm to 27.6mm. In all, the OSMW had better frying characteristics and is thus recommended for industrial purposes. Recommendations were made for further study on other potato varieties.

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