Abstract: 【Objective】 The inconsistency between external appearance and the internal quality of ‘Bingtang’ sweet orange (Citrus sinensis Osbeck) fruit has significantly reduced its marketing value. The present research intended to establish the classification standard for fruit quality and the non-destructive technologies for quality analysis and quality rating of ‘Bingtang’ orange, and then to quickly sort out the online products with different total soluble solids (TSS) and acidity. 【Method】 Fruit TSS and acid content were analyzed by sampling from the main production areas with the conventional destructive methods for a long period. The correlation among the external and internal key fruit quality parameters was calculated, and then the relationship between fruit diameter vs. TSS and acid content was determined. A standard for fruit quality classification of ‘Bingtang’ sweet orange was established. Based on the standard, the NIR transmission spectrum at 710-960 nm was utilized for fruit quality analyses, and repeated correction and verification were performed in comparison with the conventional quality analysis data to evaluate the accuracy in non-destructive fruit quality analysis and sorting. This non-destructive system was run on packing line, and the rating products were investigated in the market including the quantity, price and sold volume of different classes of ‘Bingtang’ sweet oranges. 【Result】 (1) Classification standard of ‘Bingtang’ sweet orange was established. Fruit size classification was set up based on fruit diameters: large 68-74 mm, medium 62-67 mm, and small 56-61 mm. And fruits were further classified into 4 classes based on the TSS and acid content, i.e. Super class: Birx≥14 and acidity≤0.4%, Class I: 12≤Birx＜14 and acidity≤0.4%, Class II: Birx ≥14 and 0.6%≥acidity＞0.4%, and Marketable class: Birx＜12 and acidity≤0.4%. (2) Following repeated analyses of single fruits, non-destructive analytical standards for TSS and acidity were formulated. In the 1st TSS testing experimentation, the testing range was set up between 10.1-14.9 Brix and resulted in only 26% of conformity between the non-destructive and the conventional quality analyses; when the TSS testing range extended to 10.1-16.2 Brix in the 2nd experimentation, 90% of conformity was obtained; when the TSS lowered to 9.8 Brix (testing range of 9.8-16.2 Brix) in the 3rd TSS test, the conformity remained as high as 90%. For the acidity analysis, the testing range was set up between 0.1%-1.26% at first, only 64% of the conformity was obtained; when the testing range expanded to 0.1%-1.37%, up to 94% of conformity was realized; if the testing range of acidity increased further to 1.53%, the result was 92% of conformity indicating no improvement was gained. (3) The application of the technique on packing line resulted in a sorting speeds up to 10 oranges per second, and the sorted fruits had a highest price of 48 yuan per kg. On the packing ling, annual sorting output reached 4 500 tons, valuing 91.22 million yuan.【Conclusion】The results indicated that the established non-destructive system was accurate in TSS and acidity analysis and the analytical standards covered the full range of TSS and acidity contents of all the commercial fruits of ‘Bingtang’ sweet orange. The classification with the fast, high-quality and non-destructive online determination of the internal quality of ‘Bingtang’ sweet orange on a large scale combined with the grading standard of fruit size would ensure an unified internal and external quality of the products.

Key words: ‘Bingtang&rsquo, sweet orange, non-destructive, TSS, acidity, on line quality grading