# Banana Puree Lactic Fermentation: The Role of Ripeness, Heat Treatment, and Ascorbic Acid
## 1 Introduction  
Banana is one of the most important fruit crops in the world. The Cavendish cultivar is the most commercialized banana cultivar, representing half of the world's total banana production [1]. Starting from banana as a raw material, industries produce several processed products, such as banana puree, banana pulp, and banana flour or powder. Banana puree, in particular, is one of the main processed banana products, manufactured for use by baby food, dairy, and bakery industries and widely used all over the world [2, 3]. Banana is a rich source of antioxidant vitamins (A, C, and E), calcium, magnesium, potassium, carbohydrates, fiber, and water, and its composition is highly influenced by the species, growing area, and degree of ripeness. In fact, as bananas ripen, the starch content decreases while sugar concentrations increase due to the progressive hydrolysis of starch into soluble sugars [4]. Bananas are considered to be a good fermentation substrate because of their high level of soluble sugars and high presence of prebiotic components, such as fructologosaccharides (FOS). In fact, sucrose, glucose, and fructose can be metabolizedinto lactic acid (which can act as a preservative, flavoring agent, and acidulant in the food industry) through lactic bacteria, as has been demonstrated in previous studies [5; 6; 7]. FOS, by their nature, have beneficial health effects on the human colon through stimulation of colonic lactic acid bacteria and by inhibiting putrefractive pathogens [8; 9; 10]. Thus, it is possible to obtain a symbiotic product via fermentation of a substrate, such as banana, through a probiotic strain. Industries are increasingly interested in the production of similar functional foods, responding to increased consumer interest in food and health. In addition, increasing attention is paid to non-dairy probiotic foods, such as cereals or legumes [11]. The development and production of new types of fermented product requires a thorough knowledge of both the raw material and the normal production process, in each single phase, to understand the possible influences of the process on fermentation. In particular, banana puree production involves the heat treatment of the raw material, followed by the draining; the next step is the removal of the peel and then the size reduction, as shown by [PERSON] et al. [4]. The heat treatment can affect the raw material, reducing banana browning [12], but also modifying their nutritional quality [13] and, therefore, possibly influences the fermentation process. Browning is a problem to consider when fresh fruits are processed and, for this reason, banana puree production requires a further phase, i.e., the addition of an anti-browning agent. In some industries, for example, the baby food industry, the addition of food additives is not allowed and, therefore, only natural substances can be used, such as ascorbic acid [14; 15]. However, the impact of adding ascorbic acid on fermentation parameters, such as probiotic growth or lactic acid production, must be precisely characterized. For this purpose, in this study, banana puree production was simulated at the lab-scale to verify if ripeness, heat treatment, and ascorbic acid addition have any influence on fermentation, with one variable being sequentially studied at a time. Firstly, we studied the impact of banana ripeness on bacterial growth, lactic acid production, and pH, testing second-grade (light green, breaking toward yellow) and sixth-grade (completely yellow) bananas as fermenting substrates. We identified the better raw material and used it in continued testing whereby two different heat treatments, sterilization and tundallization, were evaluated. Finally, the better ripeness grade and heat treatment conditions were used to assess the potential effect of ascorbic acid addition on the same fermentation parameters.