Modelling and optimization of production of coffee-like powder and brew from palm date seeds by roasting and grinding

A significant quantity of date seeds is being generated annually from palm date industry. This by-product is usually discarded or used as an animal fodder. However, palm dates seeds can be a potential source of nutritious elements and antioxidants which could be used for human consumption in a powder form and decaffeinated coffee-like brew. Hence, the study investigated the thin layer drying characteristics of date seeds at three roasting temperatures (160,180, and 200 ºC) and modelled the changes in color, hardness, total specific grinding energy and the oil extraction yield of date seeds during roasting process. Besides, the study aimed to investigate the influence of roasting temperature and time on the physical and sensory properties of the full fat roasted date seeds powder (RDSP) and defatted roasted date seeds powder (DRDSP). Additionally, the effect of roasting temperature and time on antioxidants, total phenolic contents, quality and sensory attributes of the full fat and defatted brews was investigated. Further, development of predictive models to estimate the properties of both RDSP and DRDSP and the proposed brews, as well as the optimization of the roasting conditions for preparation of the RDSP and DRDSP and brews were conducted. The effects of the storage conditions on the physical and flowability properties of the RDSP and DRDSP as well as the quality and sensory attributes of their brews were studied and the shelf life of the powders and brews by integrating of quality and sensory data was assessed. The study outcomes revealed that the thin layer drying characteristics of date seeds were satisfactorily described by the modified Henderson & Pabis model. While, the color parameters (L*-value and b*-value) and the hardness of the roasted date seeds can be fittingly described by the first-order equation, while a*-value and ΔE were adequately defined by the zero-order model. A decrease in total specific grinding energy and an increase in oil yield were recorded as the roasting temperature and time were increased. The physicochemical, flow, quality and sensory attributes of the products were found to be significantly influenced by the roasting temperatures and time. The models proposed could satisfactorily describe the changes in the physicochemical, flow, quality and sensory attributes of RDSP, DRDSP and the brews. The optimum conditions of the roasting process obtained using the superimposed contour plot were 199.7 ºC and 10.2 min to produce RDSP and 200 ºC and 11.2 min to prepare DRDSP. Also, the optimal roasting temperature and time were 197.98°C and 12.8 min, respectively for preparing the full fat brew. While, the optimum points for preparing the defatted brew were 199.19°C and 22.7 min. Regarding the storage and shelf life study, the results showed that the storage conditions have a significant effect on the properties of RDSP, DRDSP and brews. Descriptive models have been developed for describing the different properties and the shelf life of the powders and brews. Interestingly, the powders and brews are microbiologically stable during the storage process. The study outputs are beneficial for dryers and roaster designs, for quality control of the final product, and for determination of the suitable storage conditions. So, there is an ample scope for the emergence of new bio industries in the date growing countries towards maximum utilization of the palm date seeds in addition to efficient and effective palm date fruit waste management.

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