| Cereal breakfast is usually eaten while soaked in milk, which calls for its good ability ofmaintaining original shape and good crispness in a relatively long time. Meanwhile, thetraditional Chinese dietay habit of hot meal places high expections on the bowl life of cerealbreakfast. Focusing on bowl life in hot milk, the design of formula, optimization of processconditions and rehydration kinetics were studied in the paper. In addition, the changes ofcomponents during extrusion and effects of additives on texture were analyzed to providecertain theoretical guide for future research.and development.Firstly, eight kinds of grains were processed using two-screw extrusion cookingtechnology. The properties of extruded products were determined and compared. The oneswith good bowl life in hot milk were chosen as ingredients. Lingo was used to design the bestformula according to their different nutritions. The results showed that millet, corn, barely,wheat with better bowl life in hot milk were suitable to be the ingredients of cereal breakfast.The best formula was as follows:55%millet,25%corn,10%barely, and10%wheat. Basedon the above formula, the product was most nutritious featuring the highest essential aminoacid index（EAAI）.Secondly, the effects of process conditions, including screw temperature, moisturecontent, and screw speed on expansion ratio and texture of cereal breakfast were studied. Theresults showed that crispness and bowl life were reduced significantly with the increase ofscrew temperature（110-150℃）. As water conten（t20%-28%）increased, crispness decreasedgreatly while bowl life changed irregularly. As screw speed（70-110r/min）increased,crispness decreased while bowl life changed irregularly. According to the results ofone-factor-at-a-time experiments, the optimal process conditions were obtained: screwtemperature129.39℃, moisture content21.82%, and screw speed87.40r/min. In this context,crispness and bowl life was5.52kg·s and3.35kg·s respectively.Thirdly, the impact of extrusion on the characteristics of starch, protein and lipid wasdiscussed. Extrusion resulted in an increase in WAI, WSI and water-soluble saccharides, and areduction in total starch. DSC showed that almost all the starch had been gelatinizated.Ultraviolet absorption spectrum demonstrated that amylopectin was the primary fraction thatunderwent fragmentation during extrusion. X-ray diffraction indicated that extrusiondestroyed crystalline structure, thus leading to a declined crystallinity. Scanning electronmicrographs（SEM）showed that starch granules became rough and rock-shaped, filled withtiny holes after extrusion.Compared to the raw, the protein of extrudates showed a lower solubility, due to thedenaturation of protein. Confocal laser scanning microscopy（CLSM）indicated that proteinaggregated during processing. Furthermore, extrusion increased the ratio of β-sheet anddisulfide, accompanied by a corresponding decrease of the rest secondary structures andsulfhydryl content. As for lipid, extrusion resulted in the formation of starch-lipid complexes.Fourth, rehydration kinetics of cereal breakfast in hot milk was studied. Results showedthat all of the three models, including Peleg model, first-order kinetic model and Weibull model described the rehydration characteristics adequately. In comparison, Weibull modeldescribed the rehydration characteristics relatively best with the smallest RMSE value. As forthe change of crispness, Peleg model was better than first-order kinetic model.Lastly, the effects of colloids and emulsifiers on the texture of cereal breakfast wereinvestigated. Results showed that emulsifiers couldn’t help improve the texture of cerealbreakfast while CMC could enhance crispness and bowl life. The optimum additive quantityof CMC was3‰. |
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