Investigations into determinants of blueberry coating effectiveness

Authors: Obenland, David - Dave; LEYVA-GUTIERREZ, F - University Of Tennessee; WANG, TONG - University Of Tennessee

Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2022
Publication Date: 12/30/2022
Citation: Obenland, D.M., Leyva-Gutierrez, F., Wang, T. 2022. Investigations into determinants of blueberry coating effectiveness. Foods. 12(1). Article 174. https://doi.org/10.3390/foods12010174.
DOI: https://doi.org/10.3390/foods12010174

Interpretive Summary: Weight loss in blueberries during storage leads to shrivel, loss of firmness and a reduction in marketability. Application of edible coatings that limit water loss after harvest may be a means of reducing weight loss and prolonging storage life. Coatings that were evaluated were composed of chitosan, Semperfresh, sodium caseinate or carnauba and applied by dipping the blueberries in the individual coatings and allowing them to dry on steel screens. After drying the blueberries were packed into vented plastic containers and then stored. In season 1 the storage regime was either three or six weeks at 34 °F and in season 2 it was 3 weeks at 34 °F followed by 1 week at 50 °F and then 2 days at 68 °F. Two varieties of blueberries were tested over two separate seasons. None of the coatings were effective in preventing weight loss or shriveling of the blueberries in either season. The effects on firmness, soluble solids, and acidity were inconsistent. Coating application acted to remove the bloom on the outside of the blueberries to varying degrees. A link between loss of surface bloom on the blueberries with coating performance could not be established. Experimentation performed to better understand why the coatings did not reduce weight loss found that excessive handling during drying reduced coating effectiveness while adding an additional coat had no positive effect. If coatings are to be used for blueberries it may be that novel formulations, specifically designed for this fruit, are needed for them to be successful.

Technical Abstract: Weight loss and associated attributes such as shrivel and firmness following harvest are critical factors in determining blueberry quality after storage. As a result, various means have been evaluated that attempt to slow weight loss and maintain quality during storage, coatings being one of the most often evaluated. The initial part of this work examined the ability of some selected coatings to minimize weight loss and maintain blueberry quality during storage. In the first year of the project, 1% chitosan (CH) plus either 1% or 2% oleic acid (OA) and 1% Semperfresh (SF) were evaluated, with storage times of 3 weeks and 6 weeks at 1°C. In the second year of experimentation, 1% CH, 1% SF, 2% sodium caseinate (SC) and carnauba wax (CAR) were evaluated with a storage regime of 3 weeks at 1°C followed by 1 week at 10°C and then 2 d at 20°C to simulate storage and marketing. The same two varieties, Snowchaser and Jewel, were used for both years. None of the coatings reduced weight loss in either year, and instead sometimes enhanced it. CH, CH + OA, CAR and SF greatly altered the appearance of the berries by removing all or a part of the waxy bloom. SC also did this to some degree but was in general better in maintaining the natural appearance. CH often reduced decay, although not when combined with OA in the first season, while SC enhanced decay in ‘Jewel’ in the second season. Shrivel was not lessened by the coatings. The effects of the coatings on firmness, soluble solids concentration (SSC) and titratable acidity (TA) were inconsistent across season, variety, and storage treatment. As a result of the poor performance of the coatings, a second portion of the study consisted of experimentation to better understand why the coating did not limit weight loss. Using CH+OA as an example, it was found that increasing the amount of handling during the drying process significantly enhanced subsequent weight loss in storage relative to blueberries with minimal handling. Increasing the number of coats from one to two did not help limit weight loss. Examination of SC-coated and uncoated fruit indicated that approximately 50% of the weight loss occurred through the stem end, regardless of the presence of the coating. Experimentation was unable to show a link between coating-induced loss of bloom and coating performance. Further experimentation is needed to devise coatings that are effective for blueberries and that can be commercially viable.