3. Results and Discussion
3.1. Effect of baking temperature on proximate composition
Effect of baking temperature on the proximate composition of fortified biscuits is presented in Fig. 1. It was observed that increasing the baking temperature from 180-200 °C resulted in a significant (P 0.05) change in the quantity of total protein content between baking temperatures from 180 to 200 °C. However, further increase in baking temperature from 200 to 220°C resulted in the reduction of protein content from 19.42 to 17.64% respectively. A significant (p < 0.05) loss of protein content up to 8.6% above the baking temperature of 200 °C was hypothesized possible may due to thermal degradation of amino acids, along with other nitrogenous compounds (Hidalgo et al., 2013). Reduction in protein content up to 2.63% was also reported by Rehman and Shah (2005) in food legumes during thermal processing. Okomoda et al. (2016) also reported the effect of hydrothermal processing on the protein content of Canavalia ensiformis, similar to the present finding. Similar observations were also reported by Asif-Ul-Alam et al. (2014) in biscuit prepared with banana flour. Retort and ohmic processing also had a significant (P < 0.05) effect on the total protein content of baby foods (Mesias et al., 2016).
Carbohydrate content (50.83 to 54.43%) of fortified biscuits were found to be significantly (p < 0.05) influenced by the increased baking temperature. It may be due to changes in other compositions of fortified biscuit which is directly related to carbohydrate content (Adebiyi, et al., 2017). Similarly, ash content was also found to be increased significantly (P < 0.05), when baking temperature increased from 190 to 220 °C. As reported by Okomoda et al. (2016) the ash content of Canavalia ensiformis also found to be increasing during hydrothermal processing. Which might be due to denaturation of other compounds may result in the concentration of ash content (w/w or percent basis).
Sensory attributes of fortified biscuit baked at different temperature are given in Fig. 1. Varied significantly (p MET > LYS > HIS which were declined significantly (p ASP > ALA > TRP > VAL > PHE > SER which were recorded a total loss of 20 to 25%, respectively. Other amino acids were also affected negatively except GLY, which was recorded a total gain of 43.96%. Generally, thermal processing of proteinaceous foodstuff at higher temperature triggers the deamination and decarboxylation process subsequently degradation of its monomeric units due to its heat sensible nature (Patrignani et al., 2016). The same trends on the amino acids profile of squid fillets seafood were observed by Deng et al. (2015) during the freeze, hot air and heat pump drying. Hidalgo et al. (2013) reported that degradation of PHE in the presence of CYS and SER occurred when heated at a higher temperature of 200 °C for a prolonged heating time of 1 h and facilitated the formation of phenylacetaldehyde. Mesias et al. (2016) also reported that the amino acids profile of vegetable baby food during sterilization using ohmic heating and retort processing was significantly (P < 0.05) affected. However, increasing the GLY content with increasing the baking temperature presumed that the GLY was produced when biscuit was heated in the presence of neighbouring amino acids ASP, SER, ALA and ILE and it also partly derived from decomposition of SER (Hidalgo et al., 2013; Deng, et al. 2015; Mesias et al., 2016).
As given in table 1, the initial TEAAs of fortified biscuit baked at 180 °C was found to be an average of 1.45 times higher than its TNEAA, significantly (P < 0.05) decreased by 24.02% (from 352.40 to 267.72 mg/g) with a gradual progression in baking temperature from up to 220 °C. Results also implied that the initial baking temperature from 180 to 200 °C were less effective to TEAAs than biscuit baked at 210 and 220 °C. Assumed that it may be due to less thermal accountable amino acids at a lower temperature and further thermal degradation/pyrolysis of amines group at higher temperature and formation of higher molecular weight polyamines (Hidalgo et al., 2013). A gradual decrease in TEAA was also reported by Okomoda et al. (2016) in Canavalia ensiformis during hydrothermal processing. However, Alajaji et al. (2006) reported that the boiling and microwave cooking caused a slight increase in TEAAs (2.02%) compared to other processing techniques. In contrast to TEAA, TNEAA was found to be fairly constant at the baking temperature of up to 200 °C accounted a slight increase by two percent, moreover, increase in the baking temperature up to 220 °C displayed a significant (P < 0.05) loss of 12.09 %, respectively. A pinpoint increase in TNEAA presumed that may be due to increasing in the content of GLU during initial baking temperature and development of some flavour such as umami taste through monosodium glutamate and its nucleotides. It was also hypothesized that increasing the GLY may also resulted the same. Whereas a decrease in TNEAA was presumed that it may be due to the pyrolysis of nonessential amino acids at higher temperatures as stated earlier loss of the responsible flavour (Deng et al., 2015).
Similarly, the TSAAs was found to be fairly stable up to the baking temperature of 200 °C, however, further increase in the temperature from 200 to 220 °C displayed a significantly (p < 0.05) loss of 19.56%. TBAAs, THAAs and TAlAAs were also was found to be less impacted at initial baking temperatures, decreased significantly (p < 0.05) with further progression in baking temperature from 200 to 220 °C, were recorded a total loss of 32.93%, 11.02% and 16.53%, respectively. In contrast, an increase in the TArAAs (6.04%) and TAAAs (2.98%) contents were recorded at an initial baking temperature from 180 to 200 °C hypothesized that it may be due to the formation of polycyclic aromatic hydrocarbons and heterocyclic aromatic amines groups which are typically induced by heat. Moreover, beyond the temperature 200 °C, a fast denaturation of 20.95 and 19.42% was recorded as a consequence of the pyrolysis of these amino acids (Bartkiene et al., 2016).
3. Results and Discussion