Evaluation of fruit leathers made from New Zealand grown blueberries

Abstract

Five different cultivars of blueberries (Vaccinium sp), Blue Magic, Burlington, Jersey, Puru, and Reka, commercially grown in Canterbury, New Zealand, were used to manufacture fruit leather. The fresh fruits were pureed with ingredients (honey, pectin and lemon juice) then dried in an oven at 60°C for 8 hours. The physio-chemical, textural, proximate and mineral contents of the dried leathers were then determined on all samples.

Proximate analysis of the fruit leathers showed that they contained low fat, protein and ash and consisted mainly of carbohydrates (mean 60.4%), fibre (mean 9.7%) and water (mean 22.2%). There were few differences between the compositions of the different cultivars. The total moisture and water activity (aw) levels (mean 0.5) were low and the titratable acidity (mean 2.6% citric acid) and pH (mean 3.3) were high, suggesting that the products would have acceptable storage characteristics and would be microbiologically safe.

The 1 mm thick slices prepared from each cultivar showed acceptable physical characteristics. The texture of the five products was soft with low hardness and tensile force; the mean hardness of the five fruit leathers was 538.1 g and the mean tensile force was 18.9 N.

L*a*b* colour analysis showed that the colour of the fruit leather was lighter (mean L* value 28.5) than the corresponding fresh berry but, overall, the five different fruit leathers still retained an acceptable blue / purple colour even though the mean a* value (the redness) reduced from 7.2 to 1.7, a 76% reduction in red colour from the mean value for the fresh berries. Processing the blueberry cultivars led to a reduction in total phenolic contents (mean reduction 15%) and antioxidant activity (mean reduction 32%) for all cultivars. Among the cultivars, Blue Magic and Burlington had the highest antioxidant and phenolic contents in both the fresh and dried fruit leathers.

Sensory analysis using an untrained (consumer-type) panel of Lincoln University staff and students showed that the fruit leathers were well accepted. The two most liked fruit leathers with an overall acceptability of 5.3 (‘moderately liked’) were Puru and Reka. These cultivars were liked by panellists due to their colour, appearance, texture, stickiness, sweetness and chewiness. The lowest score was achieved by Blue Magic and Burlington, these cultivars were disliked by panellists due to their colour, overall appearance and flavour. Puru scored the highest for almost all attributes, was ‘liked’ by 38% of the panellists and had an overall acceptable of 5.0 out of 7.0. Overall, 93% of the panellists liked the fruit leathers which confirmed that it would form an acceptable new product.

Significant correlation was found between sensory attributes and instrumental parameters of the prepared fruit leathers. This research found that ORAC value was positively correlated to colour and overall appearance. Acidity was also positively correlated with hardness and tensile but negatively correlated with ORAC value.