Biological Activities of Novel Kombuchas Based on Alternative Ingredients to Replace Tea Leaves

Background/Objectives: Traditional kombucha is produced by fermenting a sweetened infusion of Camellia sinensis leaves with a symbiotic consortium of bacteria and yeasts (SCOBY). The growing interest in this beverage has driven the exploration of alternative substrates, including a wide range of plant-based raw materials, such as leaves, fruits, flowers, and seeds. Consequently, numerous products are being investigated for their differential properties, not only organoleptic but also nutritional and bioactive. This review aims to summarize recent advances in alternative kombucha research, focusing on the substrates used, their physicochemical and biochemical characteristics, and the biological activities studied. Methods: A comprehensive literature search was conducted to select articles related to alternative kombuchas. A critical analysis of their current state was carried out through the Strengths, Weaknesses, Opportunities, and Threats (SWOT) methodology. Results: The SWOT analysis led to the identification of strengths, including promising in vitro results and growing consumer interest; weaknesses, including a lack of animal studies, clinical trials, and approved health claims, and an excessive focus on antioxidant activity and phenolic compounds; opportunities, including substrate diversity, innovation, and consumer education; and threats, including elaboration risks, misinformation, competitors, and potential consumer rejection. Conclusions: Despite the promising results achieved to date, it is essential that the scientific community and the food industry continue efforts to generate robust evidence, particularly through clinical validation, in order to draw reliable conclusions regarding the benefits of alternative kombuchas for human health.