Kaki fruit as natural thickening agent in sherbets

The high pectin content and their particular composition make kaki fruit (Diospyros kaki) promising for technological exploitations as natural additive in fruit-based products. Sherbet is usually formulated with water, sugars, fruit juice and/or pulp, and thickening agents to obtain a good structure and stability. The aim of this work was to verify the possibility of using kaki pulp as a natural thickening agent in fruit sherbet production. Apricot and strawberry sherbets with different fruit content (30 and 45% by weight) were produced in order to select a reference formulation. Besides the reference (30% strawberry sherbet with no thickening agents), 30% fruit sherbets containing kaki alone or mixed strawberry-kaki were produced to verify the technological performance of kaki as thickening agent. The mixed-fruit sherbets were formulated with three different strawberry-kaki ratios (1:1, 2:1, and 5:1), maintaining a constant soluble solid content (31°Bx). Soluble solid content, viscosity and density were measured on sherbet mixes before freezing, while on the finished products overrun, instrumental firmness, melting behavior, and shape retention were evaluated. A sensory analysis was also performed to highlight creaminess and sweetness differences between reference and the various sherbets. The kaki sherbet showed lower melting rate and higher shape retention than those of strawberry reference. The higher pectin content accounts for the melting resistance of kaki sherbet and the higher viscosity of the mix before freezing. Strawberry pulp replacement with kaki fruit at 2:1 and 1:1 ratios proportionally improved sherbet melting behavior, but did not affect shape retention. The low pH of strawberry pulp (3.5 vs. 6.7 of kaki) probably modifies pectin structuring capacity. Moreover, kaki fruit sherbet was judged significantly creamier than strawberry reference.