Calendula oil processing : seed classification, oil extraction, refining process development and oil quality aspects

The difference in Calendula oil quality from fractions obtained after seed classification is enormous. The oil quality varies from excellent to very poor, according to important aspects such as in the hulls and dust fraction, high free fatty acid values (13% vs. 0.6%) are found. This can be explained by the presence of active lipase enzymes in this fraction, possibly from fungal or microbial sources. In general, Calendula oil deterioration will occur after long periods of post-harvest storage due to seed damage and unfavourable quality conditions regarding moisture, temperature and enzymatic activity. The dark oil colour is probably caused by chemical/enzymatic oxidation and hydrolyzation and is very persistent during the chemical refining steps as degumming, refining, bleaching and deodorising. Processing the oil directly after harvesting, combined with nitrogen flushing and cold storage will probably prevent the formation of a dark colour. Lab-scale refining has shown that an excellent oil quality can be produced using a good initial oil quality. The use of high temperatures (200 °C or higher) for oil deodorisation will cause modification and polymerisation and the formation of calendic acid isomers. Calendula oil is rich in gamma (1800-1900 ppm) and alpha (270 ppm) tocopherol and its content is not affected by processing or refining and is relatively high compared to other tocopherol-rich sources such as soybean or maize oil. Recovery of these tocopherols can be of interest, both as a by-product (vitamin E) and to obtain reactive oils (low in anti-oxidant). However, special care must be taken to avoid changing the reactive character of the conjugated triens present in the oil. High temperatures should similarly be avoided while developing a mild process for oil deodorisation and tocopherol removal.Chemicals/CAS: alpha tocopherol, 1406-18-4, 1406-70-8, 52225-20-4, 58-95-7, 59-02-9; gamma tocopherol, 7616-22-0