Effects of Debittering Treatments on Some Secondary Metabolites’ Bioaccessibility, Fatty Acid, and Aroma Profiles of Semidried Gemlik Variety Black Olives

Abstract

Table olives are an important component of the Mediterranean diet and are known to be highly beneficial to health due to their rich content of phenolic compounds, high levels of monounsaturated fatty acids, vitamin E, phytosterols, squalene, minerals, and fiber. However, their natural bitterness caused by the presence of oleuropein makes them unpalatable in their raw form. Throughout history, various methods have been tried and developed to remove the bitterness of olives. In this study, Gemlik variety black olives underwent a heat pump drying (HPD) process at 40°C for semidrying, followed by different debittering treatments of dry salting and brining, and then samples were stored at 4°C for 5 days. The raw olive sample was found to be the richest in total phenolic content (TPC), oleuropein content, total antioxidant activity (TAA), and total monomeric anthocyanin (TMA) content. The debittering treatments reduced TPC; especially, dry salting led to the highest loss. However, the in vitro gastrointestinal (GI) digestion process increased TPC, indicating that phenolic compounds are still being extracted and released during digestion. DPPH and FRAP values of the predigestion (Ud) samples varied between 102.62 μmol TE/g dw and 224.62 μmol TE/g dw and between 12.67 and 127.96 μmol TE/g dw, respectively. Among the table olives processed using different debittering treatments, the one stored at +4°C exhibited the highest values for TAA and TMA content. All debittering treatments led to reductions in TAA and TMA levels. However, the in vitro small intestinal-digested (Isid) samples showed variations in TAA values, with an increase observed in TAA values for all samples determined by FRAP method. Similarly, TMA values ranged from 12.74 to 30.05 mg/kg in the Ud samples, while TMA values of the samples after in vitro GI digestion ranged from 36.06 mg/kg to 103.28 mg/kg. The treatments used lead to a decrease in oleuropein concentration and an increase in hydroxytyrosol and tyrosol levels. In the evaluation of the fatty acid composition of raw and table olives, 11 different fatty acids including oleic, palmitic, linoleic, stearic, elaidic, palmitoleic, and arachidic were detected in all samples. A total of 57 aroma compounds were detected in the samples, of which 55 were successfully identified. Among the samples, the one subjected to dry salting was the most preferred in terms of sensory evaluation. These findings suggest that when reduced salt consumption is a priority, low-temperature drying process in combination with other debittering treatments can result in olives with an improved flavor and enhanced functionality, providing a healthy black table olive option for consumers.