Development of an analytical approach for determination of acrylamide content in roasted date seed varieties

Date seed are considered as a valuable by-product from Phoenix dactylifera L. which played an important role in the economy and social life of the people of the Middle East and North Africa region. They consist mostly of carbohydrates, fatty acids and proteins as well as phenolic compounds. Despite the presence of various beneficial bioactive compounds, they are usually discarded or are utilized as animal fodder. Therefore, explore the effective methods to incorporate date seeds in the human diet is a great of interest. Roasting provides a low cost and easy approach to add value to these wastes as roasted date seed powder is being used in the Arabian region to make “date seed coffee”. However, along with color and aroma changes, carcinogenic substance such as acrylamide may also formed during the roasting process. To date, no data have been published on the analysis of acrylamide in the roasted date seeds and respective brews. Therefore, the objective of the present study was development of an analytical method for determination of acrylamide in various date seeds varieties and their respective moka brews for the first time. Besides, other parameters related to the roasting process such as the color parameters and melanoidins content were also determined and compared with values obtained from Arabica coffee. 

For this purpose 5 different varieties of roasted date seeds including Shahani, Zahedi, Kabkab, Mazafati and Estamaran as well as Arabica coffee were used for coffee brewing. For acrylamide determination in solid samples, they were firstly extracted using hot deionized water. Afterwards, 5 mL of sample (extract or coffee brew) was placed in a 15 mL falcon and extraction solvents including acetonitrile (10 mL), hexane (5 mL) along with 1 g of NaCl and 4 g of MgSO4 were added. After mixing on vortex for 1 min and centrifugation (5 min, 5000 rpm), 2 mL of the supernatant was cleaned using appropriate combination of sorbents (100 mg PSA, 50 mg C18 and 50 mg SAX) along with 0.30 g of MgSO4.The cleaned supernatant was filtered and analyzed using high-performance liquid chromatography coupled with a photodiode array detector (HPLC-PDA) at 202 nm. The injection volume was 20 μL. The chromatographic separations were performed on a Eurospher 100-5 C18 column (250× 4.6 mm). Optimization was performed according to the type of organic solvent (acetonitrile and methanol), the percentage of organic solvent in the mobile phase (10, 5, 3% v/v) and the flow rate (0.1, 0.7, 0.5 mL/min). The color parameters (using photography and help of ImageJ software) and melanoidin content (spectrophotometrically at 420 nm) were also determined. 

The results indicated that the water/acetonitrile with a ratio of 97:3 and a flow rate of 0.7 mL/min permitted the acceptable separation of the acrylamide peak from the interfering compounds. The LOD and LOQ of optimized analytical method were 9.1 and 30.62 µg/kg, respectively. The suggested HPLC/PDA method is promising for analysis in order to guarantee the quality control of acrylamide. The presence of acrylamide in all roasted date seeds was observed. Accordingly, acrylamide content in Arabica coffee (1825.23± 17.44 µg/kg) was significantly higher than those obtained from date seeds varieties. The amount of acrylamide in different types of date seeds varied from 360.99± 4.15 to 129.43± 2.37 µg/kg, being Kabkab and Mazafati as the highest and lowest values, respectively. Moka brews prepared from roasted date seeds demonstrated the presence of acrylamide in the range of 25-68 µg/L. The highest level of melanoidin were observed in Arabica coffee followed by Shahani, Zahedi, Kabkab, Mazafati and Estamaran, respectively. In the most cases, an inverse relationship was observed between the acrylamide and melanoidin content in roasted date seeds. For example, Shahani had low acrylamide and high melanoidin content. The study of color parameters revealed that the parameters a* and b* largely follow the pattern of melanoidin, so with increasing the amount of a* and b*, the amount of melanoidin also increased in the samples.