Apple consumption has become a well established trend worldwide. With 86 million metric tons produced annually apples (Malus domestica) are one of the most commonly consumed fruits.
Approximately $20 billion of apple sales are generated annually in the United States. With an estimated 5 million tons produced yearly in the U.S. within the last decade.
When it comes to fresh consumption apples are the second most popular fruit after grapes in the U.S. Despite the fact that fresh consumption is the most common, 35% of consumed apples undergo some kind of processing. The majority of apples are processed for apple juice. Other products derived from apple processing include:
- jams,
- jellies,
- cider,
- vinegar,
- and dried products.
Apple Processing
There is a 75% juice extraction efficiency in the apple juice industry. Processing apples into food products leaves behind pomace – the skin, seeds, core, stems and soft tissue of the fruit. Approximately 25 to 40 percent of apples and other fruits end up as pomace, which has little economic value and pollutes the environment.
According to the U.S. Apple Association, approximately 701.4 million kg of apples were produced for juice and cider during the 2021–2022 period . Therefore, it is estimated that 175,350 metric tons of apple pomace were produced during this period according to the 75% extraction efficiency.
Where does apple waste end up?
Apple waste in its vast majority is deposited in landfills. Resulting in significant environmental impacts, as it disrupts the carbon:nitrogen ratio in soil due to modifications in: sugar content, organic acids, and the microbial fermentation of this waste product. Another deleterious factor associated with the disposal of apple pomace is its high water content, which leads to water pollution.
Considering that this by-product represents a source of nutrients like: carbohydrates, micronutrients, and phytochemicals various industries have attempted to take advantage of it, aiming to reduce its waste. THis by product can also be used for:
- pectin extraction,
- production of enzymes and aroma compounds
- cultivation of microbial strains and edible mushrooms,
- and incorporation into animal feed.
Bioactive compounds and health promoting properties
Apples are known to contain contain several health enhancing compounds. Different studies have shown antioxidant properties, antiproliferative, and anti-inflammatory effects associated with polyphenols found in apple fractions.
Some of these polyphenolic compounds found in apples are: quercetin derivatives (galactoside, glucoside, rhamnoside), catechin, gallic acid, phloretin, and chlorogenic acid. Apple seeds have found to be a rich source of quercetin derivatives, phenolic acids, catechin, and phloridzin.
The presence of pectin a non-digestible soluble polysaccharide, is also considered a health-promoting constituent. Historically utilized as a commercial thickening agent, pectin has potential functional properties that can enhance intestinal health. Its resistance to gastric digestion, allows this polysaccharide to reach host’s intestine and undergo microbial fermentation. Leading to the production of short-chain fatty acid (SCFA) and other metabolites which are beneficial to gut health.
SCFAs have been proven to boost enteric epithelial cell proliferation, enhance gut barrier function, improve micronutrient absorption, and contribute to the growth of beneficial bacterial populations.
Study
A study carried out by a group of researchers at Cornell University aimed to evaluate the in vivo effects of Empire apple juice, pomace, and pulp soluble extracts on intestinal functionality, morphology, and the microbiome of broilers (Gallus gallus).
Materials and Methods
There were five treatment groups: non-injected (NI); 18 MΩ H2O (H2O); 6% apple juice (AJ); 6% apple pomace (APo); 6% apple pulp (APu). The eggs were treated by intra-amniotic administration of the samples on day 17 of incubation. After hatching, the blood, tissue, and cecum samples were collected for further analyses—including duodenal histomorphology, hepatic and duodenal mRNA expression, and cecal bacterial populations.
Results
Researchers found that introducing apple juice and pomace into the egg contributed by:
-
enhancing the transport system for amino acids in chicks
-
improving iron bioavailability
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boosting microbial populations in the large intestine of the poult
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supporting the growth of potentially beneficial gut bacteria
Circular economy approach
“If we can potentially use the pomace, which is rich in nutrients, we can add it to the diet of broilers,” said Tako. “We can improve the nutrition in their feed and achieve productivity in a more natural way.”
Conclusions
The obtained results suggest that the tested apple fractions, have the capacity to influence gut health by modifying:
- duodenal brush border membrane functionality,
- morphology,
- and cecal microbial populations.
Apple pomace proved to be beneficial for overall health as it was shown to:
- reduce iron metabolism protein gene expression (DcytB),
- increase villi surface area and decrease crypt depth,
- increase Paneth cell count per intestinal crypts,
- increase potentially beneficial gut bacteria such as(Clostridium spp.)
Nonetheless, researchers from this study stated that further long-term studies need to carried out in order to fully understand and establish the health benefits associated with the inclusion of this apple by-product.
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