Optimization of reduced calorie kiwi jam production: physicochemical characterization and bioaccessibility in gastrointestinal conditions

Response surface methodology (RSM) was used to optimize the reduced calorie kiwi jam production under the effect of the independent variables including apple juice (X₁), stevia (X₂), and low methoxyl pectin (LMP) (X₃). The effect of these independent variables on physicochemical properties (brix, total acidity, pH), color values, total phenolic content (TPC), total antioxidant capacity (TAC), sugar profile, 5-Hydroxymethylfurfural (HMF) content, textural properties and sensorial acceptability of jam samples studied using Box-Behnken Design. Additionally the bioaccessibility of TPC and TAC for kiwi fruit and jam products was evaluated using standardized in vitro digestion model. Jam processing led to a significant reduction in TPC (51.38%–79.92%), and TAC for DPPH (85.59–96.97%), CUPRAC (60.10–82.79%), and FRAP (78.50–95.59) (p < 0.05). The TPC of all jam samples increased significantly, ranging from 1.14 to 2.67 times higher after in vitro digestion (p < 0.05), despite the total antioxidant capacity (TAC) showing variable results. The results also indicated that the addition of apple juice and stevia significantly enhanced the bioaccessibility of phenolic compounds (p < 0.05). The relationship between the responses (including brix, total acidity, pH, L*, a*, and b* values, firmness, stickiness, viscosity index, HMF, sucrose, TPC, CUPRAC, FRAP, and overall acceptability) and the variables was most accurately described using quadratic, reduced quadratic, and reduced cubic models with high R² values, as determined by RSM. The optimal condition for all responses with composite desirability of 0.877 was: 398.5 g of apple juice, 20.2 g of stevia, and 0.45 g of LMP. This study provides valuable insights into the formulation of healthier, low-calorie kiwi jams with enhanced nutritional and sensory properties, offering a promising approach for the food industry.