Have a look at this article
Source: http://www.science.edu.sg/ssc/events.js ... 68&cat=330
[Project ID: BC 03]
Bad Milk Indicators
Chong Mui Fong, Sim Wen Hui (Victoria Junior College
When milk turns bad, the consumer wants the carton to inform them so, even before the primitive smelling and tasting. Also, wastage can be reduced if the consumer knows when the milk exactly spoils instead of following the designated expiry date. Hence, this leads us to a search for a natural pH indicator for milk spoilage. pH of fresh milk decreases from approximately pH 6.8 to pH 6.2 before it curds. The curdling stage deemed the milk unfit for consumption. Next, it involves finding a source of a suitable natural indicator that can be safely incorporated into the milk carton during the manufacturing process. Anthocyanins, pigments that are found in many vegetables and fruits and changes colours with pH, are favourable choices.
Through a series of experiments, we are able to isolate the anthocyanins from red radish skins and the red capsicum. Mixing the two extracts gives an indicator solution which shows two apparent colours in fresh milk and spoilt milk. Next, we came up with a product design that enables the consumer to track freshness of milk. This involves incorporation of a dropper-like instrument containing the indicator solution, which is able to suck in milk in a single direction from the carton with a squeeze and a colour chart printed on the carton for comparison. Simple to operate, low-cost, and totally safe from contamination, its popularity will be witnessed in due time