Instrumental analysis of volatile and other compounds of Greek kiwi wine; sensory evaluation and optimisation of its composition

The production of kiwifruits is a dynamic agricultural activity in Greece. The biggest part (nearly 60%) of the total quantity produced is exported. The remainder is locally consumed, with the exception of a percentage which is not marketable due to its appearance or its being in excess of demand. To exploit this surplus of non-attractive, small-sized Greek kiwifruits, there is the possibility of wine production, which is applied in this research study. Various classic and instrumental methods (GC, HPLC, ion chromatography) and sensory analysis, in conjunction with statistical analysis, were developed in an attempt: (a) to maximize the quantity of the juice extracted from raw material, (b) to evaluate kiwi wine composition (volatile compounds, organic acids, inorganic ions, sugars, glycerol) and (c) to optimise its quality according to consumer preference. The yield of the juice is increased up to 75% in weight by using riper kiwifruits and by processing them with pectolytic enzymes. Kiwi fruits left to ripen for 3 months showed a 3 g/l acidity decrease, expressed as citric acid, and an increase in sugar content of about 2 Brix degrees. Kiwi juices were weaker in sugar than the grape musts and the produced kiwi wines were poor in alcohol content but rich in titritable acidity. Citric, galacturonic, lactic and malic acids are the dominating organic acids. In most cases, the kiwi wines' contents of aromatic components are lower in grape wine, but methanol content is higher because of the use of pectolytic enzymes. After sensory evaluation, the analysis of variance for sweetness proved significant only in the sugar effect and just marginally so in that of alcohol and CO2. Sensory alcohol is significantly influenced by sugars, alcohol and CO2, while carbon dioxide, viewed as a sensory indicator, was not found to be statistically influenced by any chemical factor examined. The statistical analyses also show that the acceptability of kiwi wines is higher if they contain 10% vol alcohol, more than 30 g/l sugars and 0.5 bar CO2.