The Science Behind Why Canned Foods Stay Fresh for So Long

Constantine Spyrou wrote . . . . . . . . .

When it comes to comparing fresh food versus canned food, one of the starkest differences between the two has to be shelf life, or how long a product can last. Most produce and meats won’t stay fresh more than a couple of days, even in the fridge or after being cooked. They’ll begin to lose flavors, change texture, and eventually spoil. Canned food, on the other hand, won’t change at all over the course of months, or in some cases, even years.

Of course, this leaves the question of how canned goods can keep for as long as they do without going bad. This has led to a number of misconceptions about the entire industry, including that they use a plethora of preservatives (not really) and are less healthy than their fresh counterparts (in some cases, canned food may actually be healthier).

Once you understand how canning works, though, it may open your eyes as to how the shelf-stable food is not only good to eat months after its made, but also why it may be, in some cases, a more nutritious option than consuming fresh food.

The History and Science of Canning

The process of canning was first invented in the early 1800s by French chef and candymaker Nicolas Appert. He developed canning as a way to preserve food using heat that won a prize from Napoleon Bonaparte, who was looking for a novel way to feed his troops. Appert first started by sealing foods in glass jars with wax. This was later shifted to tin cans, the basis of modern canning operations today.

Appert’s process was a form of sterilization, only instead of using chemicals (which is what many people recognize it as today), he was using heat to kill bacteria. This was similar to what Louis Pasteur did in 1864 when he invented the pasteurization process used in milk and juices, but Pasteur was looking to just kill pathogens, or disease-causing microbes. Other bacteria, including those that didn’t need oxygen (called anaerobes), could still grow and multiply over time.

Where Appert’s process differed was in that he used an airtight environment, as well as a greater amount of heat. This combination meant that bacteria and other spoilage microbes inside would be killed and unable to regrow. One of the biggest threats came from anaerobic bacteria that produce heat-resistant spores. The type of sterilization in canning uses enough heat to prevent these spores from ever having the chance to grow and multiply.

All of this happened without the need for preservatives that go into products like packaged cereals and other shelf-stable foods. While some canned products contain salt, sugar, or acidic products like vinegar, these are meant more for flavor, color, and texture than they are for the preservation properties they often have in foods.

Sterilization does also cook the food inside, meaning that textures will change as a result.

How Canning Changes Food

Today, canning has evolved to utilize more sturdy packaging and scientifically-controlled heat. Food processors use enough heat at an appropriate time needed to kill the requisite bacteria or spoilage organism in question. Scientists target specific microbes for each food based on its acidity, moisture content, the heat resistance of the target microbe, and other factors.

More than just keeping bacteria from spoiling food over months, though, canning has other benefits. One of the biggest is that food preserved by canning is often sterilized straight from being harvested. Over time, the nutritional and sensory qualities of food decrease over time when exposed to a normal environment. This means that technically, a peach that’s been on the shelf for a couple weeks has less available nutrients, flavor, and color than one picked fresh from the tree. Compounds naturally break down over time, so this is natural.

In canning, however, food is preserved much closer to the harvest point, and are subject conditions (including that airtight seal) that prevent degradation from occurring as fast. Thus, nutrients may be more available from a canned food compared to the fresh version in grocery stores. That’s not true for all nutrients, however. Some water-soluble nutrients like Vitamin C and some B vitamins, leach into water surrounding the food or are destroyed by heat while the food is sterilized. You’ll see a decline in these nutrients overall when cooking, regardless of process.

The next time you’re looking at purchasing canned food and judge it for being “lower quality,” as its often perceived, you might want to keep the above in mind. More often than not, canned food is just as nutritious as the fresh variety and can last a lot longer without the need for preservatives.

Source: FoodBeast

Chinese-style Lemon Chicken

Ingredients

1 lb skinned, boneless chicken breasts
1 tablespoon light soy sauce
1 tablespoon Shaoxing rice wine
1 scallion, finely chopped
1 tablespoon finely chopped ginger
1 garlic clove, finely chopped
1 egg, lightly beaten
3/4 cup cornstarch
oil for deep-frying

Lemon Sauce

2 tablespoons lemon juice
2 teaspoons sugar
1/2 teaspoon salt
1/2 teaspoon toasted sesame oil
3 tablespoons chicken stock (page 281) or water
1/2 teaspoon cornstarch

Method

  1. Cut the chicken into slices. Place in a bowl, add the soy sauce, rice wine, scallion, ginger and garlic, and toss lightly. Marinate in the fridge for at least 1 hour, or overnight.
  2. Add the egg to the chicken mixture and toss lightly to coat. Drain any excess egg and coat the chicken pieces with the cornstarch. The easiest way to do this is to put the chicken and cornstarch in a plastic bag and shake it.
  3. Fill a wok one quarter full of oil. Heat the oil to 375°F, or until a piece of bread fries golden brown in 10 seconds when dropped in the oil.
  4. Add half the chicken, a piece at a time, and fry, stirring constantly, for 3-1/2 to 4 minutes, or until golden brown. Remove with a wire strainer or slotted spoon and drain. Repeat with the remaining chicken.
  5. Reheat the oil and return all the chicken to the wok. Cook until crisp and golden brown. Drain the chicken. Pour off the oil and wipe out the wok.
  6. To make the lemon sauce, combine the lemon juice, sugar, salt, sesame oil, stock and cornstarch.
  7. Reheat the wok over medium heat until hot. Add the lemon sauce and stir constantly until thickened. Add the chicken and toss lightly in the sauce. Serve hot.

Source: The Food of China

Better Sleep? Prebiotics Could Help

Lisa Marshall wrote . . . . . . . . .

Think dietary fiber is just for digestive health? Think again.

Specific fibers known as prebiotics can improve sleep and boost stress resilience by influencing gut bacteria and the potent biologically active molecules, or metabolites, they produce, new CU Boulder research shows.

The research could ultimately lead to new approaches to treating sleep problems, which affect 70 million Americans.

“The biggest takeaway here is that this type of fiber is not just there to bulk up the stool and pass through the digestive system,” said Robert Thompson, a postdoctoral researcher in the Department of Integrative Physiology and lead author of the study, published March 2, in the journal Scientific Reports. “It is feeding the bugs that live in our gut and creating a symbiotic relationship with us that has powerful effects on our brain and behavior.”

Food for our bugs

Most people are familiar with probiotics, friendly bacteria present in fermented foods like yogurt and sauerkraut. More recently, scientists have taken an interest in prebiotics—dietary compounds that humans cannot digest but serve as nourishment for our microbiome, or the trillions of bacteria residing within us. While not all fibers are prebiotics, many fibrous foods such as leeks, artichokes, onions and certain whole grains are rich in them.

For the study, the researchers started adolescent male rats on either standard chow or chow infused with prebiotics and tracked an array of physiological measures before and after the rats were stressed.

As reported in the researchers’ previous study, those on the prebiotic diet spent more time in restorative non-rapid-eye-movement (NREM) sleep. After stress, they also spent more time in rapid-eye-movement (REM) sleep, which is believed to be critical for recovery from stress.

While rats eating standard chow saw an unhealthy flattening of the body’s natural temperature fluctuations and a drop in healthy diversity of their gut microbiome after stress, those fed prebiotics were buffered from these effects.

The new study sheds light on how prebiotics can help bust stress.

“We know that this combination of dietary fibers helps promote stress robustness and good sleep and protects the gut microbiome from disruption. With this new study, we wanted to try to identify the signal,” said senior author and Integrative Physiology Professor Monika Fleshner, director of the Stress Physiology Laboratory.

Using a technology called mass spectrometry to analyze the rats’ fecal samples, the researchers measured metabolites, or bioactive small molecules produced by bacteria as food is broken down.

They found rats on the prebiotic diet had a substantially different “metabolome”, or make-up of metabolites. Theirs was higher in dozens of them, including fatty acids, sugars and steroids which may, via gut-brain signaling pathways, influence behavior. The rats’ metabolome also looked different after stress.

For instance, the rats on the standard chow diet saw dramatic spikes in allopregnanolone precursor and Ketone Steroid, potentially sleep-disrupting metabolites, while those on the prebiotic diet saw no such spike.

“Our results reveal novel signals that come from gut microbes that may modulate stress physiology and sleep,” said Fleshner.

In search of a better sleeping pill

While prebiotic dietary fiber is certainly healthy, it’s uncertain whether just loading up on foods rich in it can promote sleep. The rats were fed very high doses of four specific prebiotics, including: galactooligosaccharides, which are present in lentils and cabbage; polydextrose (PDX) an FDA-approved food additive often used as a sweetener; lactoferrin, found in breast milk; and milk fat globular protein, abundant in dairy products.

“You’d probably have to eat a whole lot of lentils and cabbage to see any effect,” said Thompson.

Prebiotic supplements already abound on natural food store shelves. But Fleshner said it’s too soon to say whether a supplement or drug containing such compounds would be safe and effective for everyone. Depending on what their microbial make-up is, different people might respond differently.

“These are powerful molecules with real neuroactive effects and people need to exercise some caution,” she said.

Human studies are already in the works at CU Boulder.

Ultimately, Fleshner believes what they are learning in her lab could lead to a new class of options for people who can’t sleep but don’t like taking narcotics.

“Armed with this information, we might be able to develop a targeted therapeutic that boosts the molecules that buffer against stress and tamps down the ones that seem to disrupt sleep,” she said. “It’s exciting to think about.”

Source: University of Colorado Boulder

Study: Community Factors Influence How Long You’ll Live

Kristen Devlin wrote . . . . . . . . .

While lifestyle choices and genetics go a long way toward predicting longevity, a new study shows that certain community characteristics also play important roles. American communities with more fast food restaurants, a larger share of extraction industry-based jobs, or higher population density have shorter life expectancies, according to researchers from Penn State, West Virginia, and Michigan State Universities. Their findings can help communities identify and implement changes that may promote longer lifespans among their residents.

“American life expectancy recently declined for the first time in decades, and we wanted to explore the factors contributing to this decline. Because of regional variation in life expectancy, we knew community-level factors must matter,” said Elizabeth Dobis, a postdoctoral scholar at the Penn State-based Northeast Regional Center for Rural Development (NERCRD), and lead author of the study. “By analyzing place-based factors alongside personal factors, we were able to draw several conclusions about which community characteristics contribute most strongly to this variation in life expectancy.”

Life expectancy refers to the length of time a person born in a given year can expect to live. Dobis and her colleagues analyzed on a county-by-county basis how life expectancy in 2014 has changed from a 1980 baseline, using data from more than 3,000 U.S. counties.

They developed a statistical model to determine the relationship between a dozen community variables and each county’s 2014 life expectancy, while controlling for personal variables that are known to be important, such as sex, race, education, single-parent status, obesity, and alcohol use.

The community variables they examined included health care access, population growth and density, fast food restaurants, healthy food access, employment by sector, urbanization, and social capital, which measures the networks and bonds providing social cohesion among residents. They looked at each variable in isolation while holding others constant, allowing them to determine which variables independently exert the strongest effect on life expectancy.

The researchers found that a county’s 1980 life expectancy value strongly predicted variations in the 2014 value, but it didn’t account for all of the variation.

“When we controlled for historical life expectancy, we found three additional community factors that each exert a significant negative effect—a greater number of fast food restaurants, higher population density, and a greater share of jobs in mining, quarrying, and oil and gas extraction,” Dobis said. “For example, for every one percentage point increase in the number of fast food restaurants in a county, life expectancy declined by .004 years for men and .006 years for women.”

This represents a 15-20 days shorter life span for every man, woman and child in a community, for each 10 percentage point increase in fast food restaurants in a community—or a 150-200 day shorter life span if the number of fast food restaurants were to double.

Similarly, a one percentage point increase in a county’s share of jobs in the mining, quarrying, oil and gas sectors was found to decrease average life expectancy by .04 years for men (or 15 days) and .06 years (22 days) for women.

The research, which was published recently in Social Science and Medicine, also revealed several community factors that are positively related to life expectancy, including a growing population, good access to physicians, and a greater level of social cohesion.

“We were surprised by the strong positive contribution of social capital to life expectancy within communities,” said NERCRD Director Stephan Goetz, professor of agricultural economics and regional economics at Penn State and a co-author on the study. “Places with residents who stick together more on a community or social level also appear to do a better of job of helping people in general live longer.”

“Another interesting finding was that lower population density, or living in more rural areas, is associated with higher life expectancy,” Goetz said. “This suggests that living in large, densely-settled metropolitan areas, with all of their amenities and other advantages, comes at the expense of lower life expectancy, at least in a statistical sense.”

In addition to being the first life-expectancy study to include community variables in a county-level analysis, this also was the first study to statistically analyze the extent to which disparities in life expectancy are geographically clustered. This analysis revealed some striking patterns.

“We found exceptionally low life expectancies in the areas of the Pine Ridge and Rosebud Reservations in South Dakota,” Dobis said. “We found similar ‘cold spots’ of low life expectancy in the arctic and interior portions of Alaska, the Deep South surrounding the Mississippi River, and in the Appalachian regions of Kentucky and West Virginia.”

The research also revealed four “hot spots” of high life expectancy: a section of the Northeast spanning from Philadelphia to New England, southern Minnesota and the eastern Dakotas into Nebraska, an area in Colorado, and an area spanning central Idaho into the upper Rocky Mountains.

The team’s findings have important policy implications, as they suggest that certain aspects of the built environment can be changed to enhance life expectancy. For example, public places that promote social interaction could increase a community’s social capital levels, which in turn promote longer lifespans.

Source : The Pennsylvania State University

Surgery with Anesthesia not Associated with Indicator of Alzheimer’s Disease

Jay Furst wrote . . . . . . . . .

Older adults who have surgery with general anesthesia may experience a modest acceleration of cognitive decline, even years later. But there’s no evidence of a link to Alzheimer’s disease, according to new research from Mayo Clinic.

The research, published in the British Journal of Anaesthesia, examined brain scans from 585 patients, ages 70 to 91 ― 493 of whom had at least one surgery with general anesthesia. The analysis found cortical thinning in cerebral areas but no significant evidence of deposits of amyloid protein, a hallmark of Alzheimer’s disease. The cortex is the outermost layer of the brain’s nerve cell tissue, and thinning of that tissue is associated with diminished cognitive functions.

“This finding suggests that the modest cortical thinning is not related to Alzheimer’s disease pathology, but is caused by other processes,” says Juraj Sprung, M.D., Ph.D., a Mayo Clinic anesthesiologist and first author of the study. “These results are reassuring and consistent with the conclusion that surgery and anesthesia do not increase the risk for development of Alzheimer’s disease.”

The potential link between surgery with anesthesia and cognitive decline in older adults has been examined for many years, and concerns have grown as animal studies have indicated that exposure to inhaled anesthetics may be related to brain changes similar to those seen with Alzheimer’s disease.

Alzheimer’s disease is a progressive disorder that causes brain cells to degenerate and die. It is the most common cause of dementia and the sixth leading cause of death in the U.S. Also, Alzheimer’s disease causes a continuous decline in cognition and behavior that disrupts a person’s ability to function. While there is no cure, some medications can slow its progression. An estimated 5.8 million Americans are living with the disease, according to the Alzheimer’s Association.

One of the key indicators of Alzheimer’s disease is a buildup of proteins in the cortical area of the brain, which can be visualized by positron emission tomography (PET) scans. The protein deposits, called “amyloid plaques,” have a toxic effect on neurons and can precede any clinical symptoms of the disease by 30 years or more.

The Mayo Clinic study used data from the Mayo Clinic Study of Aging, which started in 2004 and has data on more than 5,000 participants ― all from Olmsted County, Minnesota, where Mayo Clinic in Rochester is located. The study analyzed 585 patients, 493 of whom had at least one surgery with general anesthesia after age 40, and later had PET scans. Of those, the median time between surgery and the PET scan was 25.9 years.

The researchers used two methods to define amyloid deposition in the PET scans. “Regardless of the definition used, no significant associations were detected between exposure to surgery and anesthesia, and increased amyloid deposition,” Dr. Sprung says.

Dr. Sprung and Mayo Clinic colleagues published a study last year that also noted the association between surgical anesthesia and cortical thinning in the signature region for Alzheimer’s disease. The study cautioned that the pathogenesis and mechanisms driving these changes required more study.

The new study concludes that the cortical thinning was not associated with pathologic changes related to Alzheimer’s, but was caused by other undetermined processes.

“Older adults who are considering surgery, and their families, must be properly informed of the risk for slightly accelerated cognitive decline in the years following surgery,” says Dr. Sprung. “However, they should also be made aware that this potential impact may be related to preexisting conditions that necessitate the surgery.”

“Most important, patients should be reassured by our findings that surgery with anesthesia does not lead to changes associated with Alzheimer’s disease,” says Dr. Sprung.

Source: Mayo Clinic


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