The effect of walnut skin extract on the physicochemical, antioxidant, textural and sensory properties of plant-based ice cream

A lactose-free walnut milk substitute was used as the main ingredient to produce a novel plant-based ice cream enriched with water/ethanol walnut skin extract (WSE). Plant-based ice cream formulations were characterized regarding their physicochemical characteristics, total polyphenol (TPC) and flavonoid (TFC) content, antioxidant activity, texture parameters and sensory attributes. The ice cream formulations with WSE had a slightly decreased pH (5.24) and titratable acidity (0.25%). The phenolic profile of the plant-based ice cream involved a TPC of 217 mg GA/100g and a TFC of 83 mg QE/100g. WSE increased the DPPH and ABTS values of the formulation by 46.89% and 89.93% in comparison with the values in the reference sample of 10.21% and 17.56%, respectively. Although the extract had an effect on the color characteristics of the ice cream, the formulation containing WSE recorded the lowest L^* index and the highest a^* and b^* indexes, at 59.23, 14.33 and 0.17, respectively. The reference sample exhibited the highest L^* index and the lowest a^* and b^* indexes, measuring 70.17, 12.76 and 0.03, respectively. The formulation with WSE had high scores for all sensory attributes (≥8.15). Notably, the formulation with WSE demonstrated a hardness value of 651.99 g, similar to that of the reference sample, at 674.46 g (P ˂0.05). The Pearson's correlations revealed the contribution of the phenolic compounds to all of the evaluated parameters. The TPC analysis achieved very strong positive correlations with DPPH (r² = 0.9792), ABTS (r² = 0.9897), hardness (r² = 0.9903) and overall sensory acceptability (r² = 0.9653), while a positive correlation was attained with pH (r² =0.7783) and TA (r² =0.7579). The implications of these results are significant for advancing the sustainable recovery of natural bioactive compounds from walnut skin within the plant-based ice cream industry.

Acknowledgments. This research was supported by Institutional Project subprogram 020405 “Optimizing food processing technologies in the context of the circular bioeconomy and climate change”, Bio-OpTehPAS, implemented at the Technical University of Moldova.