Paul McMullan and Dr. Lynn Ogden, Department of Nutrition, Dietetics and Food Sciences
My project was focused on developing a yogurt that was sweeter than traditional yogurt via means of lactose-hydrolysis. The purpose was to find what percentage of added sugar could be spared when hydrolyzing the lactose inherent in milk. The 3 batches of milk had additional sugar and Non-Fat Dry Milk (NFDM) added to boost its lactose content. The two experimental batches were treated with the lactase enzyme and left to sit for a period of 48 hours, at which point one could safely assume that 99% of the lactose had been fully hydrolyzed. One of the experimental batches had 50% of the control batch’s sugar added and the other had 100% of the sugar added.
Each of these 3 batches was then heat-shocked to 180 degrees Fahrenheit and was treated by adding the bacterial culture ABY-2C and left to sit until a pH of 4.4 was achieved. It was then rapidly cooled and smoothed. After a day of refrigeration, it had a blended strawberry fruit base added to it to achieve the desired end product. This product was served in sampled pairs to volunteer sensory panelists, who compared the control batch of yogurt (full sweetness) to differing aliquots of sweetness, ranging from 100-50% and differing by 12.5% each and each panelist received all 5 pairs to sample albeit in a different order so as not to bias them.
While carefully done, the research did not turn out how we had anticipated. We had expected that at the 87.5% or so of the normal sweetness batch, the experimental lactose-hydrolyzed batch would surpass the control in sweetness, meaning that more than half of the panelists would agree that it was the sweeter of the two. However, the lactose-hydrolyzed batch never tasted sweeter to the consumer. Even the aliquot with 100% sweetness of the original yogurt only had 18 out of 54 panelists agree that it was sweeter than the control batch.
We suspect that when the bacterial culture was added, they typically preferentially consume lactose, and because the lactose was removed via hydrolysis, there was only sucrose, glucose and galactose available. Of these sugars, it seems that the bacteria preferentially consumed the sucrose. Because sucrose is a sweeter tasting sugar, this left the lactose-hydrolyzed milk batches considerably less sweet than the conventionally prepared batch as they would effectively have an unknown quantity of their sucrose removed. While we cannot be sure as to the exact amount of sucrose consumed, the results of the panel do show a steadily increasing trend to suggest that when the % sucrose concentration rose in the experimental batches the consumers did find a corresponding increase in sweetness. Presumably only a portion of the sucrose was consumed by the bacteria.
These findings suggest that while lactose-hydrolysis may be a possible method for increasing sweetness in milk products, that it requires further testing to be successfully implemented in fermented products. The next avenue of research would be to explore different food-safe bacteria strains which could preferentially consume either glucose or galactose and spare the sucrose so as to produce a sweetertasting product. Additionally, one could also look at changing the order in which the sugars are added to the yogurt batches. In this trial, the sucrose was added before fermentation which is what led to it being consumed rather than the galactose and glucose. It would be worth studying if the bacteria can ingest glucose or galactose at all, and whether or not it then will produce the desired end products with no undesirable off-flavors.