Impact of variety and brewing method on physical and chemical properties of date seed brew

Date seed is considered as one of the most important wastes in the date processing industry which despite its high nutritional value, it is usually disposed of. This results in environmental contamination that require high cost to resolve. On the other hand, waste valorization in the food industry is important both in terms of environmental and economic benefits. Studies indicated that date seeds have a high nutritional value and could be considered as a good source of bioactive compounds (Platat, Habib, AL Maqbali, Jaber, & Ibrahim, 2014). The amount of dietary fiber in different types of date seeds varies between 20 to 80% w/w (Al-Juhaimi et al., 2018). Date seeds also contain 5.9-9.9% w/w protein (Bouaziz et al., 2008) and 5-13 w/w oil (Nehdi et al., 2010). The antioxidant properties of date seeds are also derived from its components such as vitamin E, beta-carotene and phenolic compounds. Thus, date seeds have the potential to be used as an ingredient in other foods, directly or indirectly (Al-Farsi et al., 2007). One of the relatively inexpensive ways to added value on date seed is to prepare a beverage from roasted date seed powder. The roasting process enhances the flavor of the brew, increases the shelf life of the product. It is hypothesized that roasting can lead to an alternative product for those who want to enjoy a somewhat coffee-like brew without caffeine (Fikry et al., 2019; Ghnimi, Almansoori, Jobe, Hassan, & Kamal, 2015). However, as it has been reported in terms of coffee, method of brewing and bean varieties can make a difference in the antioxidant properties of the final product (Vignoli, Bassoli, & Benassi, 2011). As a result, in this study, the effect of variety and method of preparation on the antioxidant properties of beverage obtained from roasted date seeds was investigated, which has not been mentioned so far. For this purpose, two types of date seed (Shahani and Mazafati) were used to prepare espresso, boiled and filtered brews and the results were compared with respective arabica coffee brews

Arabica coffee (Coffea arabica) and two types of Shahani and Mazafati dates were purchased from local stores in Mashhad, Iran. Three types of coffee brews including espresso, boiled and filtered brew were prepared. In this study, the antioxidant properties, phenolic and flavonoid content, caffeine, melanoidin, color parameters and pH of brews (espresso, boiled and filtered) were studied.

The phenolic content in Mazafati and Shahani and arabica coffee brews were in the range of 37-102, 41-194 and 52-328 mg/100 mL, respectively. The method of preparation also has a significant effect on the extraction of phenolic compounds, as the content of phenolic compounds in coffee increased from 52.94 prepared via the filter method to 328.33 mg in 100 ml of espresso coffee. In the present study, the total flavonoid content in Mazafati, Shahani and arabica coffee brews were 11-30, 14-68 and 32-200 mg/100 ml of beverage, respectively. The decrease in the content of phenolic as well as flavonoid content in date seed beverages can be attributed to both the lower amount of these compounds in the powders and the lower rate of their extraction. The results of Olechno et al. (2020) indicate a significant effect of the preparation method on various phenolic compounds content in coffee. The reducing power of Fe+3 in beverages obtained from Shahani date seed was almost twice that of found in Mazafati date seed. However, in all beverages, the highest reducing power of Fe+3 was found in espresso coffee (32.13 mmol Fe+2/L). Besides, the free radical scavenging power of DPPH in date seed brews were close to arabica coffee as the values in the date seeds of Shahani, Mazafati and arabica coffee (depending on the type of beverage) varied in the range of 2.66-8.79, 2.79-14.6 and 2.13-13.95 mmol Trolox/L, respectively. The results show a negligible amount of caffeine in the date seed brews as the amount of caffeine in these samples, regardless of the method of preparation, were 0.26-2.82 and 0.3-3.1 mg/100 ml, respectively. While caffeine content in coffee (regardless of preparation method) ranged from 36.90 to 75.24 mg per 100 ml of brew. The amount of melanoidins in Arabica coffee was significantly higher than those found in date seeds. This difference in melanoidins level can be seen in a variety of preparation methods. Espresso and boiled coffee brews had the highest amount of melanoidins in an insignificant manner (p>0.05). This trend was also observed in brews prepared from date seeds. The method of preparation had a significant effect on pH (p<0.05). The pH value in brews prepared from arabica coffee and Shahani date seed were as follows: filter> espresso> boiled and in Mazafati brews was as follows: espresso> filtered> boiled. Regarding color parameters, Shahani and Mazafati date seed brews were almost similar and indicated more L* than coffee brew. This proved that date seed brews are lighter than coffee brews. In general, the highest amount of L* (82.35) was observed in Shahani date seed brew prepared by filter method and the lowest amount (20.02) was observed in arabica coffee prepared by espresso method. Parameter b* indicates the range of yellow (+) to blue (-) and its value in beverages prepared from Shahani and Mazafati brews (27-37) was more than coffee drinks (17-25).

In general, although roasted date seeds brews had less antioxidant properties than arabica coffee brews, the results showed the presence of relatively moderate amounts of these compounds in date seed beverages provide high potential of use this drink in the future as healthy beverage. In addition, due to the absence of caffeine, these brews can be considered as a good option for people who are sensitive to caffeine.