A snapshot of the dairy microbiome from dairy cows to consumer food products

Dairy products house a variety of nutrients and are capable of supporting both human health and microbial life. UC Davis research offers a glimpse at the microbial life maintained by dairy milk during its production and provides clues as to how dairy food products influence human gut microbiome and health.

Dairy faces its own bacterial environment before it becomes processed. Milk can be contaminated by cow hides, food, feces, human handling and milk production equipment. Pasteurization, controlled milk heat-treatments inside of silos, aims to remove bacteria.

Mary Kable, a research molecular biologist at the United States Department of Agriculture Western Human Nutrition Research Center and associate adjunct professor in the UC Davis Department of Nutrition, worked to identify microbial communities inside of raw milk between tankard transportation and the beginning steps of pasteurization.

When raw milk is collected from dairy cows, it undergoes pasteurization, where the milk is heat-treated to remove microbes and food-borne pathogens, and then converted into dairy products.

After assessing over 800 tankards, Kable found several microbial communities surviving the first step of pasteurization.

“After pasteurization, I found that strains of Turicibacter, a bacterium found in feces, remained prevalent in milk and Staphylococcus remained in smaller quantities,” Kable said. “Overall, the quantities of bacteria that lead to spoilage did not change.”

A factor in the presence of microbial communities lies in silo cleaning.

When raw milk is pasteurized, it is concentrated in streams and separated into different dairy components: fresh milk, cream and skim milk. After pasteurization, silos are cleaned in place, or rather rinsed in place, which could miss the small nooks needed for dairy processing and leave room for bacterial biofilms to bloom.

Dairy products can be nonfermented, or maintained fresh without microbes, or fermented with select cultures of microbes for dairy processing. Nonfermented dairy products include 1 percent or 2 percent milk to increase shelf-life and avoid spoilage. Fermented dairy products can consist of cheeses, yogurts, kefir and butter.

“Fermented dairy products, like yogurt and cheese, contain lactic acid bacteria such as Streptococcus thermophilus and Lactobacillus bulgaricus, at a much higher concentration than in other foods like fruits and vegetables,” said Maria Marco, a professor in the UC Davis Department of Food Science and Technology. “The microbes grow in dairy products, consume lactose sugars and change the texture of milk into the desired fermented dairy products based on their proportions. Research shows that exposure to lactic acid bacteria improves the human immune system.”

Once consumed, the lactic acid bacteria create transient changes in the human gut microbiome, lasting for only a few days.

“A recent study of over 100,000 people from 21 different countries showed a lower disease risk, especially of the risk of stroke, for those consuming two servings of dairy per day,” said Danielle Lemay, a research molecular biologist at the United States Department of Agriculture Western Human Nutrition Research Center and associate adjunct professor in the UC Davis Department of Nutrition.

“Dairy consumption is associated with reduced risk of chronic diseases, such as osteoporosis which is a loss of bone mineral density, and cardiovascular disease,” Lemay said. “Dairy consumption also improves exercise recovery and reduces muscle loss in the elderly.”

Lemay’s research will now focus on lactose intolerant people, determining how dairy consumption shapes their health outcomes and gut microbiomes.

Written by: Foxy Robinson — science@theaggie.org

Researchers study the effects of oxytocin, alcohol, methamphetamine on pair-bonding in Titi monkeys, prairie voles

With Valentine’s Day having just passed, the topic of love is a frequent conversation starter and comes with lots of questions. What causes people to fall in love? How do close relationships form, and what causes them to end?

The answer may lie in observing monogamous animals, such as Titi monkeys and prairie voles, since they form partner bonds similar to humans.

“People often ask me if humans are monogamous and I avoid the question a little bit, but what I think is the important similarity between these other mammals and humans is that as adults both sexes can form these long term and very affiliative, selective relationships, and a lot of males do help take care of kids,” said Karen Bales, a professor of psychology at UC Davis. “These are commonalities we can study in these species that you can’t study in say a rat.”

Bales studies both Titi monkeys and prairie voles and pointed out that, in terms of relationships, humans are more attached to loved ones than these mammals.

“What is different is that humans have the capability of maintaining very close selective relationships not just with our partner but also with our parents, kids and friends,” Bales said.

“Adults (mammals) are not that attached to their kids. A way to measure attachment is whether one gets upset when someone is gone. The adult Titi monkeys do not get upset if their kids leave.”

Observations of socially monogamous mammals like prairie voles can also tell us more about what neurologically causes pair-bonding in humans.

“Studies in prairie voles have been predictive for human research: neural mechanisms that have been found to regulate pair bond formation in prairie voles have been later found to be involved in social attachments in humans,” said Andrey Ryabinin, a professor in behavioral neuroscience at Oregon Health State University.

Hormones such as oxytocin have also been shown to play a role in pair bonding in both male and female mammals.

“A lot of what I’ve done has been looking at manipulations that are developmental,” Bales said. “We’re researching how being exposed to a bunch of extra oxytocin the day a prairie vole is born effect[s] the ability as an adult to form a pair-bond.”

Bales also studies the effects of oxytocin on non-human primate mammals, such as Titi monkeys.

“We have been doing experiments where we give a little extra nasal oxytocin or temporarily block oxytocin and looking at changes in females,” Bales said. “We studied the males first and now our current funding is to study the neurobiology of pair-bonding in female Titi Monkeys, and I expect there will be differences.”

Ryabinin is also studying the effects of drugs and alcohol in prairie voles in an effort to see the effects of these substances on pair-bonding.

“In these studies, the drugs were not simply administered to the animals by an experimenter without any control by the animal,” Ryabinin said. “Instead, our prairie voles were voluntarily self-administering the drugs. Most of our studies have been with alcohol, but some also examined the effects of methamphetamine. We found that voluntary alcohol consumption had an unexpected sex-dependent effect on pair bonding. Alcohol inhibited pair bonding in males but enhanced it in females. In contrast, methamphetamine inhibited pair bond formation in both male and female prairie voles.”

Ryabinin has concluded that different substances affect pair-bonding through slightly different mechanisms, and his lab is currently studying those mechanisms.

On a different note, research that is based solely on human relationship formation and how we select our partners is also currently being conducted at UC Davis.

“Generally speaking, relationship initiation is a pretty extensive and lengthy process,” said Paul Eastwick, an associate professor of psychology at UC Davis. “It’s a process that can take anywhere from months to years. This is even true in the modern technological age.”

Eastwick also studies ideal partner preferences, which are sets of traits humans say they value and want their partner to have.

“Traits can include things like attractiveness, ambition and trustworthiness,” Eastwick said. “There is general agreement that these traits are positive. But other than that individual differences in who says they care about what particular quality, say you care about attractiveness and I care about ambition, is basically uncorrelated with how much attractiveness and ambition ultimately appeal to your immediate romantic partner. People don’t seem to have a lot of insight into the traits that are uniquely appealing to them.”

Eastwick also explained how certain inherent factors or situations dictate how we select romantic partners.

“If you live in a part of the country that is more religious, for example, you’re more likely to date people that are religious.”

On top of this, people generally tend to date people who are similar to them in terms of levels of attractiveness, a concept known as assortative mating.

Ultimately, relationships among both humans and animals are areas of extensive research and both neurological and social aspects of our lives may affect how we form bonds with partners.

Written by: Jessica Montross — science@theaggie.org

Study finds shorter sleep durations lead to a decrease in EEG waves

In a recent study restricting sleep durations in adolescents, the UC Davis Sleep Lab found that shorter sleep durations led to a significant decrease in waking EEG power. This is just one part of the laboratory’s long history of looking at sleep in adolescents.

According to Ian Campbell, the associate project scientist in the department of psychiatry and behavioral sciences, the Sleep Lab started its adolescent studies in 2002 when they initially began looking into how sleep and EEG brain waves change across childhood and adolescence.

“What was special about that study, what made it different from all previous studies, is that it was longitudinal,” Campbell said. “So we followed the same people over time. Previous studies had been cross-sectional, so they compared the brain waves of like a nine year old to a 15 year old and would look at how they were different. By following the same kids over time, we are able to very precisely determine how sleep and the EEG brain waves change across adolescence.”

The study found that total sleep time between the ages of nine and 18 decreased by approximately 10 minutes per year, which was correlated with a decline in the time they spent in bed. The decline in total time in bed was not caused by earlier waking times, but rather by going to sleep later. Hans P. A. Van Dongen, the director of Sleep and Performance Research Center and professor of Elson S. Floyd College of Medicine at Washington State University, has also studied studied the effects of sleep and sleep deprivation on performance and came to similar conclusions.

“Sleep need is not the only aspect of sleep that changes with age – so is the optimal timing of sleep,” Van Dongen said. “This applies to adolescents who have trouble getting out of bed in the morning – they are not “lazy” as is often assumed, just aren’t ready to wake up yet in the early morning hours. And it also applies to older adults, who may gradually wake up earlier and earlier in the morning and think they cannot get enough sleep anymore – but may actually get more sleep if they would also go to bed earlier in the evening than they may have been used to.”

Campbell also said that the research found that this decrease in sleep duration was entirely in non-rapid eye movement sleep, with an increase in REM sleep. In addition, although Campbell and his team had prior knowledge that children have more slow wave activity than adults, they were unsure whether this was a gradual or abrupt change.

“We were particularly interested in these big slow waves because these big slow waves are an indicator of a type of recuperation that happens during sleep,” Campbell said. “If somebody has been awake longer, they will have more of this slow wave activity. If somebody takes a nap in the afternoon, then they will have accomplished some of the night time recuperation during that nap and they’ll have less of that slow wave activity at night.”

The longitudinal study showed that slow wave activity was fairly constant between the ages of six and 12, but their delta power plummeted from there until age 16. Campbell stated that he thinks that during this period, the adolescent brain changes in a way that there is a decreased need for recuperation throughout sleep, which may be driven by synaptic pruning. By comparing females and males, the team found that this change occurred earlier in females, a finding they attributed to puberty, though they are unsure whether puberty causes the EEG change or if a mechanism upstream triggers both occurrences.

“We did not think it was going to be related to puberty,” Campbell said. “We thought these were two totally independent things, that sexual maturation was one thing and the synaptic pruning that’s causing the EEG changes was something different. There’s was no reason for them to be linked in time and [we were] surprised that they were.”

With this portion of their study ending in 2012, Campbell and his team are currently running a dose-response study determining whether sleep need decreases, increases or remains unchanged throughout adolescence and into early adulthood.

There have been various previously conducted studies that looked into sleep need in adolescents. Mary A. Carskadon, professor of psychiatry and human behavior at Alpert Medical School of Brown University and director of chronobiology and sleep research at EP Bradley Hospital, published an article June of 2011 titled “Sleep in Adolescents: The Perfect Storm” about how adolescents’ loss of sleep is not driven by a lower need for sleep, but rather a combination of biological, psychological and socio-cultural influences. She believes that many people have misconceptions about adolescents being able to obtain an adequate amount of sleep by going to sleep earlier.

“For many teens this is just not feasible, given the biological process that are also reinforced by modern ‘conveniences’ that provide reasons to stay awake late,” Carskadon said. “That said, if we lived by the rule of daylight and darkness, which of course we do not, the issues would not manifest as they now do. On the other hand, I suspect that adolescents would still carve out a temporal niche that is later than that inhabited by grown ups.”

In Campbell’s current study, participants are assigned to spend either seven, eight and a half or 10 hours in bed and then come into the laboratory for performance testing, which is then compared with their prior sleep duration. The researchers will follow these participants over time to discover whether this relationship changes with age. In their most recently published paper, “shorter sleep durations in adolescents reduce power density in a wide range of waking electroencephalogram frequencies.” They found that from 10 hours in bed to seven hours in bed, waking EEG power declined significantly. As they have already conducted studies on individuals from ages 10 to 14, Campbell hopes that by studying people of ages 15 to 20 they will be able to attain a more firm answer on how daytime performance is related to age and how this changes with age.

“This idea that sleep is not important, that I can stay up all night and study and still perform well the next day is not a good approach to life,” Campbell said.  

Written by: Michelle Wong — science@theaggie.org