Meat-free minerals: the mineral content, bioaccessibility, and bioavailability of iron and zinc vegetarian and vegan burgers

In a recent study published in Nutrients, researchers compared the mineral content and absorption of plant-based meat-free (vegan and vegetarian) burgers and beef burgers.

Study: Content and Availability of Minerals in Plant-Based Burgers Compared with a Meat Burger. Image Credit: NatashaPhoto/Shutterstock.com
Study: Content and Availability of Minerals in Plant-Based Burgers Compared with a Meat Burger. Image Credit: NatashaPhoto/Shutterstock.com

Background

The world is transitioning towards plant-origin diets from animal-origin ones, given their ability to lower the risk of obesity, cardiovascular diseases, and type 2 diabetes. Although iron stores may be low among vegetarians, the incidence rates of anemia among vegetarians and vegans do not significantly differ from those among non-vegetarians. Therefore, a well-planned, varied vegetarian diet could maintain optimal iron nutrition. Additionally, plant-based diets improve the microbial balance and diversity of the gut microbiome.

However, there have been concerns regarding whether plant-based diets can match omnivorous diets regarding the content and absorption of calcium, iron, zinc, n-3 fatty acids, vitamin D, and vitamin B12. Since these nutrients are abundant in animal-based products, vegan and vegetarian diets need professional guidance to prevent dietary deficiencies.

About the study

In the present study, researchers compared the mineral content and bioavailability of minerals in plant- and animal-based burgers.

The team sourced the burger samples from a supermarket in the United Kingdom (UK) and cooked them using a grill or an oven. Subsequently, the burgers were freeze-dried for 5.0 days and blended to form fine powders, which were stored at 5.0°C. The moisture content of the dry powders was analyzed by placing them in crucibles at 65°C for two days until a constant weight was achieved and reweighing the samples.

Mineral content (calcium, copper, iron, magnesium, manganese, and zinc) was quantified using inductively coupled plasma-optical emission spectrometry (ICP-OES) following microwave digestion. The team assessed the bioavailability of minerals in vitro based on gastrointestinal simulations concerning food digestion, and the mineral uptake was evaluated by exposing the human colorectal adenocarcinoma (Caco-2) cell line to the burger samples.

In addition, the protein content in the Caco-2 cell lysate was determined using bovine serum albumin as a reference. Data were expressed as means and compared using the one-way analysis of variance (ANOVA) test. In addition, post-hoc tests were performed for multiple comparisons using beef as the control. Data were considered statistically significant if the p-value obtained was below 0.05.

Results

The mineral content significantly varied among the burgers. The plant burgers mainly comprised pumpkin, beetroot, mycoprotein, red cabbage, jackfruit, potato, and soy. The moisture content of raw burgers ranged between 51% and 78%, while that of cooked burgers ranged between 48% and 75%. The vegetarian/vegan burgers comprised more calcium, magnesium, copper, and manganese compared to the meat burgers.

The beef burgers comprised significantly more zinc and iron than the plant burgers. In addition, iron bioaccessibility was significantly greater among beef burgers than most plant-origin substitutes; however, the bioavailability of iron was similar in both types of burgers. Likewise, zinc bioaccessibility and bioavailability were significantly greater in the anima-based burgers, with only the mycoprotein-based plant burger demonstrating similar zinc bioavailability, as per previous studies.

Among plant-origin burgers, those comprising beetroot and pumpkin contained iron in comparable amounts as beef burgers, whereas burgers comprising soy protein comprised four-fold more iron (15 mg of iron per 100 g) than beef burgers. However, iron bioavailability from beetroot burgers was significantly lower than from beef burgers.

The finding of higher calcium content in plant-based burgers than beef burgers followed the National Diet and Nutrition Survey (NDNS) findings and could be due to the calcium chloride (CaCl2) incorporation in plant-based burgers to improve firmness and wheat flour fortification with calcium. The findings indicate that plant-based alternatives could be important calcium sources for non-consumers of dairy products, fish, or meat.

Soy lowers the bioaccessibility of iron due to iron encapsulation within large-sized peptide conglomerates during digestion in vitro. Nevertheless, soy fortification with vitamin C in sufficient amounts could, in part, overcome the effects of soy on the bioaccessibility of iron. Additionally, the baking procedures performed during burger preparation may partially reverse iron inhibition by the soy protein. The comparable levels of iron bioavailability in plant-based and beef burgers may be due to the various food constituents additionally incorporated into the burgers.

Conclusions

Overall, the study findings showed that beef was a better source of biologically accessible iron and zinc than most plant-origin alternatives, whereas vegetarian/vegan burgers contained more calcium, copper, magnesium, and manganese than beef burgers. The amount of biologically accessible and absorbable iron varied markedly in the plant-origin burgers.

The meat alternatives could provide zinc and iron in sufficient quantities to individuals consuming them as components of varied diets. Therefore, guiding health choices would depend on the varieties of vegetable components and the nutritional quality of iron in the different burgers. However, the content does not precisely estimate bioavailability; therefore, the total content of minerals may not be commensurate with their bioavailability and bioaccessibility.

Journal reference:
Pooja Toshniwal Paharia

Written by

Pooja Toshniwal Paharia

Pooja Toshniwal Paharia is an oral and maxillofacial physician and radiologist based in Pune, India. Her academic background is in Oral Medicine and Radiology. She has extensive experience in research and evidence-based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.

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