Production of Syrups from Corinthian Currant Industrial Finishing Side-Stream: Quality Evaluation and Volatilome

Abstract

The industrial finishing side-stream (FSS) of premium-quality Corinthian currants was used to produce syrups with/without pigment- and tartrate-reduction treatments. The chemical composition, total titratable acidity (TTA; % w/w as tartaric acid), volatile acidity (VA; % w/w as acetic acid), total phenolic content (TPC; as gallic acid, GA), antioxidant capacity (AC; as ascorbic acid, AA), volatilome (SPME GC-MS), sensory properties, and microbial stability were compared. All syrups had similar average sugar content (65.4–69.4% w/w), and no sucrose. Those not treated for tartrate reduction were more acidic (pH ~4.5) than those treated (pH > 5.6), while all syrups had higher pH than similar commercial products (3.0–4.5). On the other hand, the FSS syrups had similar TTA (<1.2 ± 0.3%) despite the applied treatment, and had low VA (0.08–0.27%). The blonde syrups had a lower average TPC (134–143 mg GA/100 g) and AC (0.90–1.0 mg AA/100 g) than the brown syrups (185–213 and 0.3–0.6, respectively), due to the removal of phenolics in the clarification treatments. Totally 144 headspace aroma volatiles were identified, deriving either from the grapes or the raisin-drying process. HMF was not detected. The sensory, microbiological, and VA analyses indicated that FSS can be used to produce high-quality, preservable, and added-value syrups.