Study on the effects of different parameters on physicochemical and thermal properties of Kabkab date powder: Optimization of the temperature effect and anti-sticking agents

The date palm (Phoenix dactylifera), is one of the most important plants of arid desert area of the western and southern Asia and northern Africa for over 5000 years. Date fruit has a great importance in nutrition due to being a main source of carbohydrates, but it is low in fat and protein. Also it is a good source of many minerals and high amounts of antioxidants which prevent some diseases. This fruits is an important element in economy of date growing countries. Some factors such as variety, environmental impact of growing regions and large quantities of the produced date causes postharvest losses resulting in lower quality fruits. These amounts of fruit which are not consumed directly as fresh may have been used as raw materials to formulate some products like date syrup, powder, jam, etc. Date powder is a highly nutritional quality sweetener obtained from date for sucrose substitution in confectionary, bakery or ice cream industry. Stickiness is a problem in production of fruit powder during drying, transportation and storage. Stickiness in fruit powder is mainly due to the presence of low molecular weight sugar such as fructose, glucose, sucrose and organic acids in fruits. These compounds are very hygroscopic in the amorphous state and have low glass transition temperature and leads to increase stickiness and decrease stability of the product in room temperature. This research consisted of two major i) determination of an optimum proportion of date paste, silicon dioxide and maltodextrin and the most suitable temperature of drying; ii) characterization of physicochemical and thermal characteristics of date powder.
Kabkab date was purchased from local market of Kazeroun, Fars, Iran. Moisture, ash, protein, fat, total sugar and dietary fiber contents were determined by AOAC methods (AOAC, 1997). Date flesh was minced by a kitchen meat grinder to make a smooth paste. Three different proportions of maltodextrin (35, 45 and 55% w/w) and three proportions of silicon dioxide (0, 0.75 and 1.5% w/w) were added to date paste to produce date powders. The mix was then spread to a thickness of about 5 mm on a Teflon coated tray and kept inside an oven dryer at 50, 60 and 70°C. The dry product was then ground in a hammer mill to produce date powder. The powder was immediately collected in plastic pouches and kept in desiccators to avoid moisture absorption from the air. Laboratory test sieves were used to collect date powder with particle size less than 1mm in diameter. Some physical and thermal characteristics of the powders were measured. Response surface methodology with central composite design was applied to minimize total number of experimental runs and to optimize the proportions of maltodextrin and silicon dioxide and also drying temperature. The dependent variables were density, moisture and color parameters. A completely randomized design was applied to analyze the effect of maltodextrin on thermal properties (glass transition temperature and specific heat) of date powder. Significant terms were found using ANOVA (P