The application of Fourier transform near infrared (FT-NIR) spectroscopy in the wine, fruit and dried fruit industries of South Africa

[摘要] ENGLISH ABSTRACT:This study shows Fourier transform near infrared (FT-NIR) spectroscopy's applicationon wine, fruit and dried fruit for quantitative determinations or as a discriminativemethod for classification purposes.During wine production optimum yeast growth, resulting in healthy alcoholfermentation rates, is monitored by the amount of free amino nitrogen (FAN) presentin the must. The status of malolactic fermentation (MLF) in Chardonnay wines ismonitored by determining the degree of conversion of malic to lactic acid. Ethylcarbamate (EC), a suspected carcinogen, is mainly formed during ageing of wine andis restricted by legislation in some countries. It is therefore necessary to determinethe EC content in wine.Fourier transform near infrared spectroscopy can be used on wine as a rapidmethod to measure the °Brix (residual sugars) content of must and to discriminatebetween different must samples in terms of their FAN values. It can also be used asa rapid method to discriminate between Chardonnay wine samples in terms of theMLF status and between table wine samples in terms of the EC content. Calibrationswere derived and it was found that a very strong correlation existed in the sample setfor the FT-NIR spectroscopic predictions for °Brix (r = 0.99, SEP = 0.31%), but poorercorrelations for the FAN (r = 0.405, SEP = 275%), malic acid (r = 0.64, SEP = 1.02%),lactic acid (r = 0.61, SEP = 1.35%) and EC predictions (r = 0.47, SEP = 3.6%). Whensoft independent modelling by class analogy (SIMCA) was applied as a discriminativemethod, the must and wine samples were classified in terms of their FAN and ECvalues and MLF status, respectively, obtaining results with recognition ratesexceeding 80%.The canning of peaches has become a significant industry in South Africa,producing approximately 4.1 million cartons per year. Fourier transform near infraredspectroscopy was applied as an alternative non-destructive method for thequantitative determination of the total soluble solid (TSS) content of whole freshpeaches. The TSS content of fresh clingstone peaches is an indication of the internalquality, maturity and perceived sweetness of the fruit for the peach canning industry.By determining the TSS, fresh peaches can be graded and the farmers compensatedaccordingly. Results obtained by building QUANT+™calibrations for the TSS content(r = 0.96, SEP = 0.55%) showed acceptable accuracy and can replace the presentdestructive methods.Peak periods during the harvesting season necessitate storage of peaches forup to three weeks before canning. Approximately 5 - 10% of the peaches stored,disintegrate during canning due to loose skin, large stone cavities, soft flesh and rot.The storage potential of fresh clingstone peaches can be successfully predicted withFT-NIR and SIMCA models, using subjective internal quality evaluations. Results withrecognition rates exceeding 80% were obtained in most cases and this methodproved useful as a non-destructive method of quality assessment. By applying thismethod, losses caused when storing peaches with poor storage quality will bereduced.The golden sultana industry plays an important role in the dried fruit exportingmarket of South Africa. Due to the large numbers of consignments that must bechecked upon arrival, and the need for rapid decision making during processing, it isessential to replace the present time-consuming analytical methods. Fouriertransform near infrared spectroscopy was used as a rapid, analytical technique todetermine whether the S0₂ and moisture contents of sultanas are withinspecifications upon arrival at the factory and during processing. High positivecorrelation was found between the measured values and those predicted by FT-NIRspectroscopy for S0₂ (r = 0.99, SEP = 24.09%) and moisture (r = 0.99, SEP =0.051 %) contents.

[发布机构] Stellenbosch University