E-News Exclusive
Apple Pomace: A Functional Food?
By Heather Davis, MS, RDN, LDN
As we say farewell to summer and welcome fall’s briskness and change of color, one fruit might be at the forefront of your mind: the apple. Apples of all varieties can be found year-round in most local supermarkets; however, fall is the time when apples shine their brightest. Once you enjoy a fresh, in-season apple, it’s impossible to forget.
Apples are the fourth most consumed fruit crop in the world.1 Although it’s hard to match the desirability of the whole, fresh fruit at the peak of its season, it’s the juice of the apple that accounts for the biggest consumer demand where apple products are concerned. During the production of apple juice, an estimated several million tons of apple pomace is generated.1 Unfortunately, there aren’t many avenues available for putting this nutrient-rich byproduct to use, and the vast majority ends up directly in a landfill, leading to more environmental concerns. Buried in a landfill, apple pomace’s high water content and biodegradable organic load tend to result in unpredictable fermentation, microbial decomposition, and a growing potential health hazard.1 To help address this problem, food scientists are exploring alternate routes for using this nutritionally dense byproduct as a functional ingredient in the food industry.
Nutritional Benefits of Apple Pomace
What’s in apple pomace? Apple pomace is almost always a mixture of skin (95%), seeds (2% to 4%), and stems (1%).1 Depending on the type of apple and the processing method, the concentration of bioactive compounds and nutrients may vary. The apple pomace carbohydrates mostly consist of insoluble fiber like cellulose, hemicellulose, and lignin; soluble fiber in the form of pectin; and simple sugars like glucose, fructose, and galactose.2 Small amounts of minerals like magnesium and phosphorus are also present.1 Apple pomace boasts a high percentage of antioxidant polyphenols (31% to 51%) in the form of flavonoids.1 Flavonoids, which occur abundantly in many plant-based foods, have several subgroups, which include chalcones, flavones, flavonols, and isoflavones.3
Apple pomace is rich in quercetin, a well-studied flavonol associated with cardiovascular health benefits, immune support, and anti-inflammatory action.4 Several studies have also demonstrated that apple pomace may help in the prevention and management of constipation and even hypertension.1 Getting creative, food scientists experiment with adding apple pomace to an array of foods, including baked goods, dairy products, meat, and beverages.1
Functional Performance
When using apple pomace as a functional ingredient, it’s a delicate balance. Researchers seek to harness the potential health benefits while identifying the point at which additional pomace leads to declining consumer satisfaction with products in areas of texture, taste, and other sensory points.
Apple pomace may play an impactful role in fiber enrichment. Pectin, the soluble, fermentable fiber found in pomace, functions as a gelling agent, emulsifier, and thickener in various food products such as jellies and jams, yogurts, and beverages.5 In addition, pomace fiber extract can be used as a fat replacement in meat products, which may improve emulsion stability and reduce caloric energy density without compromising satiety.1
Baked Goods
Many experts have experimented with adding pomace to breads, cakes, cookies, muffins, scones, and other baked goods. For breads, they found that a 3% to 5% pomace addition scored well in sensory measures of odor, taste, and texture and helped reduce the hardness and staling progression.1 Above 5%, sensory scores dropped, and favorability declined. In some cases, apple pomace at less than 20% was successfully used as a wheat flour substitute in muffins, scoring high on tests for color, texture, and taste.1
In addition to improving the flavor, apple pomace boosted fiber and total phenolic content, including antioxidant activity, in these products.1 One study noted that a 20% inclusion of apple pomace in scones led to a three- to four-fold increase in total phenolic content and total flavonoid content.6 In another study, apple pomace at 20% was shown to reduce the glycemic index of cookies from 70 to 60, enhancing the nutritional value without compromising the sensory quality of the cookies.7
Dairy Products and Meat
In products like yogurt, the addition of 3% apple pomace not only provided additional fiber and polyphenols but also was found to shorten the fermentation time and contribute to a more consistent and firmer yogurt gel, acting as a natural stabilizer and texturizer.1 However, more tests using apple pomace in dairy products are needed to confidently determine consumer acceptability.
In one study where the meat level of buffalo patties was substituted with 2% to 8% apple pomace, authors discovered improvements in fat percentage, moisture, and crude fiber without compromising the cohesiveness of the patty. The sweet spot for best results appeared to be around 6% apple pomace.1
Similar studies have used apple pomace substitutions in mutton and chicken nuggets, chicken sausage, and a traditional Kashmiri meatball called mutton goshtaba, with pleasant improvements in textural properties.1
Beverages and Mushroom Cultivation
Apple pomace can be fermented to produce ethanol, developing mild alcoholic beverages with enhanced flavor. This process has been used for many years, as it’s a low-cost option with minimal land requirements.1
Another lesser-known way to use apple pomace is in the cultivation of edible mushrooms. Rich in carbohydrates like lignin and essential nutrients encouraging mushroom growth like nitrogen, apple pomace may support a variety of mycelia, including shiitake and oyster mushrooms. One study tested a growth substrate of pomace and sawdust separately and in combination, demonstrating a higher yield was produced on pomace alone than on sawdust.1 Adding 2.5% pomace increased mycelial growth rates in solid and liquid cultures by 34.5% and 20%, respectively. However, more pomace isn’t always better; beyond 5%, pomace was found to negatively impact mushroom growth.1
Concerns and Risks
There isn’t enough data yet to account for every potential risk associated with apple pomace. However, existing studies focus on two main areas of concern: natural plant toxins and pesticide or fungicide residue exposure.1
Apple seeds contain amygdalin, which is a natural cyanogenic glycoside that can lead to cyanide poisoning if consumed in sufficient amounts.1 However, recent research has suggested that around 800 g of apple pomace would need to be consumed to reach toxicity levels.8 That’s a lot of pomace! For most people, they’d likely never eat enough to reach those numbers.
As far as pesticide concerns, several studies have evaluated neonicotinoid and acetamiprid residues in apples, and in these cases, levels were found to be negligible in terms of health impact, though more studies may be warranted.1 Beyond pesticides, fungicides are also commonly used in apples to improve the quality and yield. Some common types of fungicides include thiophanate, carbendazim, and pyrimethanil.1 The Environmental Protection Agency weighs in on these fungicides, regarding them for the most part as low-risk for acute toxicity.8
Overall, more studies are needed to explore this question of contamination risk, including considering novel pesticides and other compounds coming to market over time and perhaps lacking updated safety data. Given that pomace holds promise for greater inclusion in the food supply as a functional ingredient and yet often represents the area(s) of the fruit with the greatest accumulation of pesticides and fungicides, it makes sense to conduct ongoing studies that affirm these early suggestions of safety.9
— Heather Davis, MS, RDN, LDN, is editor of Today’s Dietitian.
References
1. Lyu F, Luiz SF, Azeredo DRP, Cruz AG, Ajlouni S, Ranadheera CS. Apple pomace as a functional and healthy ingredient in food products: a review. Processes. 2020;8(3):319.
2. Dhillon GS, Kaur S, Brar SK. Perspective of apple processing wastes as low-cost substrates for bioproduction of high value products: a review. Renew Sustain Energy Rev. 2013; 27:789-805.
3. Panche AN, Diwan AD, Chandra SR. Flavonoids: an overview. J Nutr Sci. 2016;5:e47.
4. Aghababaei F, Hadidi M. Recent advances in potential health benefits of quercetin. Pharmaceuticals (Basel). 2023;16(7):1020.
5. Chandel V, Biswas D, Roy S, Vaidya D, Verma A, Gupta A. Current advancements in pectin: extraction, properties and multifunctional applications. Foods. 2022;11(17):2683
6. Reis SF, Rai DK, Abu-Ghannam N. Apple pomace as a potential ingredient for the development of new functional foods. Int J Food Sci Technol. 2014;49:1743-1750.
7. Alongi M, Melchior S, Anese M. Reducing the glycemic index of short dough biscuits by using apple pomace as a functional ingredient. LWT-Food Sci Technol. 2019;100:300-305.
8. Skinner RC, Gigliotti JC, Ku K.-M, Tou JC. A comprehensive analysis of the composition, health benefits, and safety of apple pomace. Nutr Rev. 2018;76(12):893-909.
9. Naman M, Masoodi FA, Wani SM, Ahad T. Changes in concentration of pesticide residues in fruits and vegetables during household processing. Toxicol Rep. 2022;9:1419-1425.