The variations in major aroma compounds in ‘Olinda' Valencia orange (Citrus sinensis) during storage

Abstract:  【Objective】Valencia orange is one of the major types of sweet orange (Citrus sinensis) , but its aroma character is not well-studied. It is essential to study the variation in volatile compounds in fresh fruits during storage. For this purpose, we investigated the variation pattern of the major aroma compounds in‘Olinda'Valencia orange during three months of storage.【Methods】Fruit materials were harvested from a local commercial orchard. The fruit were immersed in mixed preservatives (5 g bellkute, 5 mL prochloraz and 1 g 2, 4-D dissolved in 20 L tap-water) for 1 minute and dried in air, and then packed in nano-plastic bags and stored under 7 ℃ for three months. Non-treated fruit stored at the same temperature served as the control. Sampling was conducted every 7 days. Decay rate and fruit weight were recorded during storage. Peel color was analyzed on six points in the equatorial region of each fruit with a Minolta Chroma Meter (CR-400, Konika Minolta, JPN) and expressed in the international CIE 1976 L* a* b* color space, where L*indicates lightness, a*indicates green to red, and b*indicates blue to yellow. Citrus color index【CCI=1 000×a*/ (L*× b*) 】, which was widely used in the citrus industry, was calculated to express the results. Total soluble solids (TSS) and total acids (TA) content were determined using a digital refractometer (PAL-BXIACID1, Atago, JPN) . Aroma compounds wereextracted and detected by head space-solid phase microextraction (HS-SPME) combined with GC-MS (2010 Qplus, Shimadzu, JPN) , and the relative content of individual compound was quantified by internal standard method.【Results】Fruits treated with a mixture of three preservatives combined with nanoplastic bagging showed a significantly lower decay rate and fresh loss than the other treatments. In addition, a lower CCI value of treated fruit was observed, which suggested that fresh-keeping treatment might delay the senescence of fruit. At the end of storage, TSS content of treated fruit was significantly lower than that of the control fruit, while TA content showed little difference. In this study, a total of 73 aroma compounds were detected, which mainly consisted of monoterpenes (16) , sesquiterpenes (22) , aldehydes (11) , alcohols (6) , esters (4) and other compounds (14) . Among these volatile components, dlimonene, β-myrcene, valencene, decanal, octanal and β-linalool were the predominant compounds.During the whole storage period, the total content of aroma compounds decreased continuously, and the peak value (104 741.91 μg·g^-1) appeared at the 7 th day of storage. The total content decreased by68.99% at the end of storage time. We found that the contents of different types of volatile compounds and their numbers changed during the three months of storage. (E)-Citral, citronellol, terpinolene, etc.were detected only occasionally, while β-citronellal, α-terpineol, cis-β-ocimene, etc. existed throughout the whole storage period. The relative contents of aldehydes, alcohols and monoterpenes decreased significantly on the 7 th day of storage, and a degradation“turning-point”of monoterpenes was observed again at day 63 during the storage, whereas sesquiterpenes slightly increased after three months of storage. The variation patterns of the relative contents of the predominant compounds were also different.After three months of storage, the relative contents of d-limonene, β-myrcene, decanal, and octanal decreased obviously, but valencene increased basically and β-linalool was relatively constant during the whole storage time. The major aroma compounds (except valencene) of‘Olinda'Valencia orange treated by the mixture of the three preservatives combined with nano-plastic bagging showed an opposite variation trend compared with the cold stored fruit within the first 28 day, but tended to be consistent after 28 day of storage. After 63 day of storage, the fresh-keeping treatment had no significant effect on the variation pattern of the major compounds. Besides, d-limonene and β-myrcene in treated fruit decreased sharply at 63 day of storage, which was consistent with the control. The variation pattern of valencene under the mixed treatment was more or less the same with the control, but the peak value of treated fruit was observed at 42 day of storage, while that of the control fruit occurred on day 28.【Conclusion】The variation patterns of different types of aroma compounds of‘Olinda'Valencia orange under storage conditions were investigated systematically in details. A degradation“turning-point”of monoterpenes such as d-limonene and β-myrcene was observed at 63 days of storage in fruit treated by preservatives or under cold storage. It is worth further study. Apart from this, we found that a mixed treatment with different preservatives combined with nano-plastic bagging maintained the basic sensory quality of‘Olinda'Valencia orange during storage, and significantly inhibited the variations in the major aroma compounds during the first month of storage.