At 5:45 AM, the doorbell rings and you swear at the milkman who is prompt in his duty to deliver the milk as early as possible. But why should you be rude to him when he is helping? HELPING?! How?!.
As you know, milk must taste both sweet and plain without any other odour, flavour, or after taste. Excessive exposure to sunlight or high-intensity light (620nm) which are common in stores could change flavour characteristics, more than so the microbial content naturally accumulates and end up spoiling the milk. This defect is known as the Light-induced flavour or lightly oxidised (reaction between the light and milk nutrients). One of the probable reasons as to why most of the milk deliveries happen either before the sunrise or after the sunset.
How will this affect the quality of the milk?
Light initiates degradation of protein due to which we can sense the burnt protein taste, more likely similar to medicinal or burnt plastic flavour. There will be a loss of Vitamin A, C, and Riboflavin. Exposure to sunlight for as little as 10–15 minutes is sufficient to cause the defect, while longer exposure times required for fluorescent lighting. The closer the milk is to the fluorescent light source or the more intense the light, the quicker the development of the off-flavour. The defect is more common in milk packaged in transparent plastic or glass, although it can also occur in milk in more opaque containers subject to very intense light for long times. Milk products like- cheese, ghee, butter, and oil — go rancid when exposed to excessive sunlight (Photo-oxidation). Consuming a rotten product may result in accelerated ageing, tissue damage, brain cell damage and development of cancer diabetes and Alzheimer’s disease in the long run. One of the sole reasons why beer and olive oils are all packaged and sold in dark-tinted glasses so that it prevents light-induced degradation.
How a Low Pass Filtered lights can affect the vitamins in milk. (Image from Noluma.com)
How can this be prevented?
It requires the milk to be stored entirely away from the sunlight. For this, one must ensure that the milk should be stored in a translucent plastic or glass bottles. The display lights in the stores should not be closer to the milk cartons. The use of shatterproof lightings/ yellow shielding can prevent and reduce the light intensity. Milk stacking in the stores should not be close to the light bulbs. LED lights used for display cases and coolers should be the “warm white” variety, which generally have less harmful energy in the critical wavelengths than the “cool white” range. Unnecessary lighting in coolers and display cases should turn off during times of the day when the milk turnover rate is slow (e.g., night shift or when the store is closed). Though the convenience of plastic containers is attractive to most consumers, light-oxidized defect is more common in this type of packaging when compared to paperboard, so extra care needed during transport and storage. Plastics containing light blocking agents or colouring (e.g., yellow) are currently used by some companies to protect their products from light-activated off-flavours and vitamin degradation. Preferable plastics used for packing of milk are grade no. 5 Polypropylene, which is sturdy, translucent and protects from light. Lastly, protecting milk from the sun should not end at the store. Consumers should also be aware that milk needs to protect from the sun during transport (e.g., offer a brown paper bag), storage and use.