Impact of Thermal Processing and Storage on the Quality and Chirality of Linalool in Blueberry Juice

Blueberry juice is valued for its distinctive flavor and health-promoting bioactive compounds, but thermal processing and subsequent storage can alter its quality and aroma. While previous studies have focused on total volatile profiles, the behavior of chiral aroma compounds-particularly linalool enantiomers-during processing and storage remains poorly understood. This study aimed to investigate the effects of pasteurization (PT, 90 °C for 30 s) and ultra-high temperature processing (UHT, 135 °C for 6 s) on the physicochemical properties, bioactive compounds, antioxidant activity, volatile profiles, and sensory characteristics of blueberry juice during storage at 4, 25, and 35 °C for 4 weeks, with a special emphasis on the enantiomeric changes in linalool. A chiral column-based GC-MS method was established to quantify (R)- and (S)-linalool enantiomers, given their distinct odor thresholds and sensory contributions. The results showed that both thermal treatments ensured microbial safety, but UHT caused greater color deterioration, loss of phenolics and anthocyanins, and formation of off-flavor compounds. PT better preserved color, bioactive components, and natural fruity aroma. Storage temperature was the dominant factor driving quality decline, with 4 °C significantly retarding deterioration. Notably, the two thermal processes exhibited distinct mechanisms affecting chiral linalool stability: PT primarily induced isomerization of (R)-linalool to the (S)-form, leading to a gradual decrease in the R/S ratio, whereas UHT led to direct degradation of (R)-linalool, resulting in a more rapid shift in the R/S ratio under the same conditions. These findings highlight the importance of monitoring enantiomeric composition rather than total linalool content for flavor quality assessment. The combination of PT and refrigerated storage (4 °C) is recommended to maximize overall quality retention, as PT better preserves the natural chiral balance of linalool. This study demonstrates that appropriate thermal processing and low-temperature storage are effective strategies to maintain the quality and chiral flavor stability of blueberry juice, providing new insights into the role of enantiomer-specific changes in processed fruit products.