A milkman puts banana leaf in milk jar, because banana leaf

A milkman puts a banana leaf in a milk jar primarily to preserve the milk by altering its chemical environment and providing antimicrobial protection. Banana leaves contain various bioactive compounds, including polyphenols, flavonoids, and tannins, which exhibit significant antibacterial and antifungal properties [t2][t4]. These compounds help inhibit the growth of spoilage-causing microbes like yeast and certain bacteria [t2]. Furthermore, the chemical interaction between the leaf and the milk tends to make the milk slightly more basic (alkaline), which slows down the natural acidification process caused by lactic acid bacteria [c2][t5]. By maintaining a more basic pH and utilizing its natural antimicrobial metabolites, the banana leaf acts as a natural preservative, extending the shelf life of the milk by making it resistant to fermentation and yeast growth [t1][t5].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC9962436/
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Table 2.3 Some naturally occurring acids > p. 28
3. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC9525789/