Traditional thermal treatment performs best for vitamin C retention in fruit juice: a pilot study using strawberry nectar

Fruit juices and beverages are rich in water-soluble vitamins, making vitamin retention a critical quality factor. Newer processing methods, such as high-pressure processing (HP), ohmic heating (OH), and pulsed electric field (PF), are believed to retain vitamins better than traditional thermal treatment (TT) due to shorter processing times and lower temperatures. However, recent reviews comparing the effects of TT, HP, OH, and PF on juice quality reveal that the available knowledge is incomplete and, at times, inconsistent.

The study uniquely presented a systematic and comprehensive comparison of the effect of four commercially relevant preservation technologies (TT, OH, PF, and HP) on all major water-soluble vitamins and color retention in strawberry nectar using pilot-scale equipment. The study’s use of pilot-scale equipment provides a standardized comparison of these preservation technologies, enhancing the relevance of the findings for practical applications.

The results indicated significant differences between the processing techniques. Interestingly, the ascorbic acid (vitamin C) content increased significantly after OH, PF, and TT treatment, with the most profound 15-fold increase observed for TT-treated nectar. The increase in ascorbic acid content was attributed to its release from the bursting of intact cells under heat stress during TT and OH treatment or electroporation during PF treatment.

Dehydroascorbic acid (another form of vitamin C) levels remained mostly unchanged after TT and PF but significantly decreased after HP and OH. In terms of total vitamin C retention, TT-treated samples performed the best after processing and after eight weeks of storage at 4°C, followed by OH, PF, and HP treatments. The greater vitamin C loss in HP-treated samples is likely due to high residual enzyme activity. 

The B vitamins remained largely unchanged after processing, with the highest loss of 34 % for riboflavin in OH-treated samples. The B vitamin content increased during eight weeks of storage at 4 °C for most samples, potentially due to the release of vitamins from their bound forms in the matrix due to residual enzyme activity.

All preservation technologies yielded similar color retention immediately after treatment and during eight weeks of storage. While the results presented in the study can be corroborated by objective evidence from the literature, the authors recommend further subjective evaluation using puree-derived nectars as they are an interesting matrix to study due to higher proportion of constituents like fiber, pectin, and other phytochemicals that can alter the behavior of bioactive compounds i.e. vitamins.

 See the full study here: Zia H et al (2024) Comparing the impact of conventional and non-conventional processing technologies on water-soluble vitamins and color in strawberry nectar - a pilot scale study. Food Chem 463: 141078. https://www.sciencedirect.com/science/article/pii/S0308814624027286