Though maintaining the quality of a beverage may be a top priority to manufacturers of functional beverages, pricing and branding plays a great role in influencing the manufacturer’s packaging decision.
“One of the biggest trends within packaging formats over the past few years has been more single-serve, sleeker bottles,” Laura Klibanow, marketing director of beverage think tank Imbibe told NutraIngredients-USA. “Glass is perceived as more premium compared to aluminium, especially in [carbonated soft drinks].”
But glass doesn’t just excel in coming off more refined than its PET counterparts—it may be better at preserving the contents’ nutrients than the ubiquitous PET bottle. “A strong degradation of ascorbic acid was noted after 3 months of storage—up to 54 at 72% of initial amount in glass and PET bottles respectively,” the researchers wrote in their study, published in the journal Food Control. Ascorbic acid, a popular source of vitamin C, is found in many fortified, bottled beverages on the market.
The studied beverage
For this study, the researchers used a multi-fruit and multi-vitamin juice supplied by Laiterie de Saint Denis de l’Hotel, composed of apple, pineapple, orange, grape, pear, peach, mango, apricot, banana, guava, kiwi, and lemon.
After dilution in some water, the team added sugar, citric acid, and a mix of vitamins C, A, B1, B6, and B9. “The juice was intentionally fortified with vitamin E (a-tocopherol) to observe the interactions between vitamin C and E,” they added.
Then, the juice was packed in either a PET or glass bottle using a semi-automatic filler. For the former, a standard monolayer PET was used. It had a 25cl capacity weighing 14g and 150 microns thick. The PET bottles were closed by caps in polyethylene and polypropylene without any internal joint, while the glass bottles were closed by metallic caps.
Observing and measuring
Bottles were stored at around 20 degrees Celsius and in total darkness. Dissolved oxygen, ascorbic acid, B-carotene, and A-tocopherol contents were monitored.
Among the many things researchers tracked and analysed were the amount of oxygen and oxygen transfer rate in both beverages. Analyses were carried out just after packing for dissolved oxygen, and then at different times of storage: 22, 37, 77, and 97 days.
“Just after filling, the initial concentration of dissolved oxygen was very low in PET or glass bottles, proving the good control of oxygen ingress during the filling process,” they wrote. But as time passed, they saw steep declines of dissolved oxygen, with “surprisingly no significant differences observed between both packages.”
However, the ascorbic acid degradation was “clearly stronger in PET comparing to glass bottles,” the researchers wrote. “As previously suggested, it was certainly due to the ingress of oxygen through PET.” Moreover, B-carotene was also oxidized in a higher extent in PET compared to glass bottles, which had a delayed oxidation because isomerisation was prevailed.
Competing for refrigerated shelf-space
“The consumption of multivitamin juice could participate to the antioxidant daily intakes if the storage in the product in the food system doesn’t exceed 2 months [in both PET and glass bottles],” the researchers concluded.
“From a nutritional point of view, the juice packed in glass bottles [contain] a higher amount of antioxidant during the course of storage and could be a healthier source of bioactive compounds,” they added.
It should be noted though that in this study, the beverages were kept at 20 degrees Celsius, which is room temperature. This is often what both manufacturers and retailers resort to, as Klibanow explained: “Refrigerated products are also perceived to be “fresher” but then (from a brand perspective) you are dealing with limited shelf-space and a more expensive supply chain.”
Source: Food Control
Published online ahead of print, doi:10.1016/j.foodcont.2015.07.039
Changes in nutritional value of a multi-vitamins fortified juice packed in glass and standard PET bottles
Authors: Céline Bacigalupi, Aurélie Maurey, Naïma Boutroy, Stéphane Peyron, Sylvie Avallone, Pascale Chalier