The aroma of Sicilian red garlic of Nubia as affected by drying methods

Introduction Garlic (Allium sativum L.) and garlic supplements are one of the oldest food flavoring also used for centuries in folk medicine for its antioxidant, anti-inflammatory, antimutagenic, antihypertensive effects1. These biological activities can be mainly recognized to many organosulphur compounds deriving by S-(2-propenyl)-1-cysteine-S-oxide due to the enzyme allinase. Nubia garlic is traditionally cultivated in the western Sicily (South Italy), mainly within the municipality of Paceco, in the Integral Natural Reserve of Saline. Despite its valuable quality, Nubia garlic is mainly traded as fresh product on the local market. However, the manufacturing of processed garlic products could rise new perspectives for its valorization by reaching markets far from the places of production. The aim of the research was to assess the effects of two different drying methods, namely hot air- and microwave-drying, on the quality and the amount of aroma volatile compounds, with particular attention to those exhibiting a biological activity. Materials and Method Fresh red garlic of Nubia bulbs, harvested during the 2017 crop season, were supplied by a local producer in May 2017 and used in the experiments. Volatile aroma compounds were determined both on fresh and dried samples. Dried samples were obtained using: 1) a tray dryer at 70 °C per 60 min; 2) a microwave oven at 400 W per 3 min. Volatiles have been analyzed by Headspace-Solid-Phase-Microextraction (HS-SPME), using a 50/30-μm film thickness DVB/CAR/PDMS fiber, coupled with a Gas-Chromatograph-Triple Quadrupole Mass Spectrometer (Shimadzu GC 2010 Plus-TQMS 8040). Each volatile compound was identified using mass spectral data, NIST’ 17 (NIST/ EPA/NIH Mass Spectra Library, version 2.3, USA) and FFNSC 3.0 (Shimadzu) database, linear retention indices (LRI), literature data and the injection of standards were available. Results / Discussion / Conclusion More than one hundred volatile compounds were identified, mainly sulfur compounds followed by aldehydes, alcohols, terpenes and esters. Qualitative and quantitative differences resulted among fresh, air-dried and microwave-dried samples. Diallyl disulfide was the most abundant compound in all samples, even if in a different amount. The dehydration processes determined an increase of the total amount of monosulfides, trisulfides, tetrasulphides and of almost all the classes of cyclic sulphur containing compounds. Opposite, the total amount of disulfides decreased after dehydration; in particular, diallyl disulfide and allyl-(E)-1-propenyl disulfide, generating by the action of allinase on allicine, resulted the main volatile compounds in fresh samples. In dried samples, diallyl sulfide, diallyl trisulfide and diallyl tetrasufide, 1,2-dithiolane, 2-vinyl-4H-1,3-dithiin, 3-vinyl-4H-1,2-dithiin and 5-methyl-1,2,3,4-tetrathiane prevailed. They are considered key compounds for the garlic aroma and their anti-cancer activity against prostate epithelial cells has been dimostrated2. These compounds also showed beneficial effect on diabetes mellitus, anti-microbial, antiviral, anti-inflammatory and cardiovascular effect3. The amount of trisulfides, tetrasulfides, thiophenes, thiolanes and of the cyclic octaatomic sulfur compound resulted statistically higher in the microwave-dried samples if compared with the air-dried ones. Since it has been demonstrated that the pharmacological activity of allium sulphur compounds increase when the number of sulphur atom increase4, the microwave drying method could be a more efficient technology than hot air-drying not only for reducing the processing time but also for enhancing the benefic health effects of garlic. Bibliographic References 1. Bayan L, Koulivand PH, Gorji A (2014). AJP, 4: 1-14. 2. Borkowska A, Knap N, Antosiewicz J (2013). Nutr cancer, 65: 711-717. 3. Hussein HJ, Hameed IH, Hadi MY (2017). Res jour pharm tech, 10: 4069-4078. 4. Wu CC, Sheen LY, Chen HW, Tsai SJ, Lii CK (2001). Food chem toxicol, 39: 563-569.