Sustainable Use of Tomato Powder Derived from Food Waste in Yogurt Formulation

The valorization of food processing by-products is a key strategy for advancing sustainability in the agri-food sector. This study developed a fermented milk product incorporating tomato powder (TP) obtained from surplus tomatoes not meeting retail appearance standards. Four yogurt formulations were prepared containing TP (2% and 4%, w/v) and two controls with skim milk powder adjusted to equivalent total solids. Samples were inoculated with a commercial starter culture and fermented at 42 °C to a final pH of 4.6. TP addition did not hinder fermentation but altered acidification kinetics, as the 4% TP yogurt exhibited a faster initiation (T_m ≈ 80 vs. 120 min in the control) yet a slower rate of pH decline (V_max = 0.009 vs. 0.019 pH units/min). TP-fortified yogurts exhibited higher water holding capacity (98% vs. 83%), increased firmness (87 g vs. 47 g), and substantially elevated viscosity (63,000–68,000 mPa·s) while lycopene enrichment enhanced color attributes. Viable counts of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus remained within typical ranges (~6.8 and ~4.9 log CFU/g, respectively, after 24 h), confirming that TP did not compromise microbial activity. Overall, incorporating TP improved structural and functional properties while simultaneously providing tomato-derived antioxidants and promoting a sustainable, circular utilization of surplus tomato streams in fermented dairy products.