Olajide P. Sobukola

Thin Layer Drying Process of Some Leafy Vegetables under Open Sun

Open sun drying experiments in thin layers of crain-crain (CC), fever (FV) and bitter (BT) leaves grown in Abeokuta, Nigeria were conducted. The drying process took place in the falling rate period and no constant rate period was observed from the drying curves. Eight thin layer mathematical drying models were compared using the multiple determination coefficients (R2), reduced chi-square (χ2) and root mean square error (RMSE) between the observed and predicted moisture ratios. Accordingly, Midilli et al. model satisfactorily described the drying curves of the three leaves with R2 of 0.9980, χ2 of 2.0×10-4 and RMSE of 1.09×10-2 for CC leaves; R2 of 0.9999, χ2 of 2×10-6 and RMSE of 1.11×10-3 for FV leaves; and R2 of 0.9998, χ2 of 1.9×10-5 and RMSE of 3.3×10-3 for BT leaves. The effective diffusivity was found to be 52.91×10-10, 48.72×10-10 and 43.42×10-10 m2/s for CC, BT and FV leaves, respectively.

Optimization of Blanching Conditions Prior to Deep Fat Frying of Yam Slices

The effect of low-temperature blanching and frying time at a frying temperature of 170°C on moisture and oil contents, breaking force and colour of yam chips was investigated using response surface methodology to establish the optimum blanching conditions and frying time. A central composite rotatable design was used to study the effects of variation in levels of blanching temperature (60–80°C), blanching time (1–5 min) and frying time (2–6 min) on quality attributes of yam chips. The effect of blanching temperature and frying time was more significant than the time of blanching on the quality attributes. The response variables were fitted to predictive models applying multiple linear regressions. Statistical analysis with response surface regression showed that moisture content, oil content, breaking force and L* (lightness) parameter were significantly (P < 0.05) correlated with blanching temperature and time and frying time. However, the regression equation showed a poor fit for a* and b* respectively. The optimum conditions were a blanching temperature of 70–75°C, blanching time of 4–5 min while frying for about 5 min.

Optimization of processing conditions for vacuum frying of high quality fried plantain chips using response surface methodology (RSM)

Optimization of processing conditions (temperature 122 to 136°C, vacuum pressure 9.91 to 19.91 cmHg, and frying time 3 to 9 min) during vacuum frying of plantain chips was investigated using a Box-Behnken experimental design with response surface methodology (RSM). Models for various responses were developed and optimized frying conditions using numerical solutions were established. Optimized vacuum fried samples were compared with atmospheric fried samples based on the concept of equivalent thermal driving force (ETDF). Frying parameters had significant (p<0.05) effects on the moisture content, texture, and color with a coefficient of determination (R2) for quadratic model responses varying between 0.53 and 0.99. Optimum vacuum frying conditions for plantain chips were a frying temperature of 133°C, vacuum pressure of 9.91 cmHg, and frying time of 6 min based on desirability concepts. Vacuum fried plantain chips had more acceptable sensory properties, based on ETDF values, than atmospheric fried samples.

Water Sorption Isotherms and Crispness of Fried Yam Chips in the Temperature Range from 293K to 313K

Water sorption isotherms of fried yam chips were determined using a static gravimetric method with saturated salt solutions in the range of water activity between 0.22 and 0.85 at 293, 303 and 313K. Four sorption models namely GAB, Peleg, modified Mizrahi, and BET were fitted with the sorption data generated. The GAB model followed by Peleg and modified Mizrahi models were found to best represent the experimental data in the aw range of 0.22–0.85. However, the BET model was more applicable between aw range of 0.22–0.55. The adsorption isotherm of fried yam chips clearly showed the influence of temperature, decreasing the moisture content at a fixed water activity value with higher temperature. The net isosteric heats of sorption of water were estimated by applying the Clausius–clapeyron equation to the adsorption isotherms at different temperatures. The net isosteric heat of sorption was observed to be decreasing as moisture content increases. Samples stored in desiccators of 0.44 and 0.55 aw at 303 and 313K, respectively, were rated higher in terms of textural properties investigated.

Effect of Frying Treatments on Texture and Colour Parameters of Deep Fat Fried Yellow Fleshed Cassava Chips

Effects of frying treatments on texture (hardness) and colour parameters () during deep fat frying of yellow fleshed cassava root slices (TMS 01/1371) were investigated. Slices (dimension of 40 mm 25 mm 3 mm) were divided into three portions and subjected to vacuum frying (fresh slices) and atmospheric frying (fresh and predried slices) and equivalent thermal driving forces (ETDF) of 60°C, 70°C, and 80°C were maintained during frying. The quality attributes investigated were best preserved in vacuum fried chips. The overall colour change in chips fried under vacuum conditions at 118°C and 8 min was the least (21.20) compared to fresh and atmospherically predried ones (16.69 and 14.81, resp.). A sharp reduction in the breaking force was obtained for all frying treatments after 8 min and this effect was the least in vacuum fried chips. First-order kinetics modeled the changes in quality attributes for all the temperatures investigated. Rate constants (min−1) obtained for vacuum frying were almost equal to that of atmospheric frying while activation energies for hardness and colour change were 53.30 and 467.11 KJ/mol, respectively. Quality attributes studied were best preserved during vacuum frying.

Evaluation and Optimization of Steam and Lye Peeling Processes of Sweet Potato (Ipomea batatas) using Response Surface Methodology (RSM)

Abstract Sweet potato of uniform sizes and shape were subjected to steam peeling (temperature 80–100°C and peeling time 5–15 min) and lye peeling (sodium hydroxide concentration 8–12%, temperature 80–100°C and peeling time 3–5 min). Response surface methodology was used to analyze and optimize the process parameters in each case. For steam peeling, the peel loss and unpeeled surface area were 6.85 and 28.16%, respectively, while optimum peeling conditions where temperature and peeling time of 100°C and 5 min, respectively, for minimum peel loss and unpeeled surface area. For lye peeling, however, the peel loss and unpeeled surface area were 13.19 and 13.35%, respectively, and optimum peeling conditions were lye concentration, temperature and peeling time of 8.89%, 100°C and 4.75 min, respectively, for minimum peel loss and unpeeled surface area. The models developed in each case (R-squared of 0.9225 and 0.8428; 0.5929 and 0.8346) were adequate in producing responses as a function of the independent variables. From the optimized values and results obtained, lye peeling was more suitable for sweet potato.

Nutrient composition, functional, and pasting properties of unripe cooking banana, pigeon pea, and sweetpotato flour blends

Abstract This study investigated some quality attributes of unripe cooking banana (UBF), pigeon pea (PPF), and sweetpotato (SPF) flour blends. Simplex centroid mixture design was used to obtain 17 blends from the flours. The nutrient composition, color, and functional properties of the blends were evaluated using standard methods. Data were subjected to analysis of variance and treatment means were compared using Duncans multiple range test at 5% probability level. There were significant (p < .05) differences in the nutrient composition, and functional and pasting properties of the blends. The crude protein, crude fiber, ash, foaming capacity, emulsion capacity, and least gelation capacity of the blends increased as the PPF level increased. The blends had Na/K ratio of <1.0. The dispersibility, bulk density, water, and oil absorption capacities of the blends increased as SPF and UBF increased. The peak, setback, and final viscosities increased as UBF and SPF inclusion increased,whereas pasting temperature and time increased as the PPF level increased. The L*, a*, and b* values of the flour blends which were significantly (p < .05) different ranged from 79.58 to 102.71, −0.15 to 2.79, and 13.82 to 23.69, respectively. Cooking banana‐pigeon pea‐sweetpotato flour blends are desirable for alleviating malnutrition in Nigeria and developing new food formulations.

Effect of species, pretreatments, and drying methods on the functional and pasting properties of high‐quality yam flour

Abstract The study investigated the functional properties of HQYF (high‐quality yam flour) from tubers of four dioscorea species. The tubers were processed into HQYF using two pretreatments (potassium metabisulphite: 0.28%, 15 min; blanching: 70°C, 15 min) and drying methods (cabinet: 60°C, 48 h; sun drying: 3 days). Significant differences (P < 0.05) were observed in pasting characteristics of flours among the four species. The drying method significantly affected only the peak viscosity. The interactive effect of species, pretreatment, and drying methods on the functional properties was significant (P < 0.05) except for emulsification capacity, angle of repose, and least gelation concentration. The significant variation observed in most of the functional properties of the HQYF could contribute significantly to breeding programs of the yam species for diverse food applications. The pastes of flour from Dioscorea dumetorum pretreated with potassium metabisulphite and dried under a cabinet dryer were stable compared to other samples, hence will have better applications in products requiring lower retrogradation during freeze/thaw cycles.

Frying of Food: A Critical Review

ABSTRACT Deep fat fried foods are very popular food because of their unique quality characteristics. The process is based on the immersing food at high temperatures, depending on the raw materials, thereby leading to physical and chemical changes such as starch gelatinization, protein denaturation browning, and crust formation. In order to obtain a product with a low fat content, it is essential to understand the mechanisms involved during the frying process so that oil migration into a food product can be minimized. The purpose of this study is to review literature findings on frying of food. The review also aims to draw the attention of stakeholders, including decision makers, on the need to assess the health risks associated with consumption of fried food product and, consequently, the necessary measures and steps to reduce such risks in order to have safer food in the world.

Quality Attributes and Storage Stability of Bread from Wheat–Tigernut Composite Flour

ABSTRACT This study was carried out to investigate the effects of wheat flour substitution with tigernut flour in bread production. Bread was baked from the composite flour and was analyzed for proximate composition, physical properties, and sensory quality, while staling characteristics were determined on composite bread samples stored for four days. There were significant differences (p < 0.05) in the proximate composition of bread samples. The physical properties of the bread decreased with addition of tigernut flour. Sensory quality decreased with increase in tigernut flour inclusion for all the attributes. As substitution of tigernut flour increases, the hardness of the composite bread increases during storage days. Crust moisture increased, while crumb moisture decreased during storage. Incorporation of tigernut flour into wheat flour led to a reduction in oven spring, loaf weight, loaf volume, specific volume, and crumb moisture, with a corresponding increase in hardness, crust moisture, fiber, and mineral content. However, tigernut flour could be incorporated up to 8% level in the formulation of bread without affecting its overall acceptability.