onions can be a part of the dough formulation or as a topping on a variety of baked goods.

Onions

Also known as Allium cepa L.


What are Onions?

Onions are a mass-cultivated vegetable that grows producing bulbs, and has been eaten worldwide for more than 4,000 years.1 They are natural flavorings used in various forms, both fresh and processed.

Traditionally, snacks have included onion for flavor. In baked products, they can be included in the dough formulation or as a topping on baked goods, such as focaccia or bagels. Onions come in many varieties, including:

  • Spanish
  • Red
  • White
  • Green

Origin

The genus Allium is the most diverse in the Mediterranean region. However, China and India are the largest onion-producing countries in the world. Generally speaking, onions require cool climates and are best grown in high altitude regions. They are available in various sizes, colors (white to red) and total soluble solids (TSS).2

Although some are perennials, they are mainly cultivated as a biennial. They are propagated by seeds, bulbs or sets.  Although an onion grows underground, it is not a root tuber. It is the shoot portion that is developed to store nutrients for the plant.1,2 

Function

Onions are characterized by their distinct aroma and flavor. Also, by their pungency, due to various sulphur-containing amino acid derivatives and aromatic structures. Most notable aroma compounds are isothiocyanates, monosulfides, disulfides, and trisulfides.2,3,4

In the food industry, onions function as flavoring agents and aroma enhancers. Similar to garlic, they contain antimicrobial actives which can inhibit growth and production of toxins by many bacterial pathogens. Allicin (diallyl thiosulfinate: thio-2-propene-1-sulfanilic acid-5-allyl ester) is the major antimicrobial component of onions and garlic. It is formed by the action of the enzyme alliinase on the substrate alliin [S-(2-propenyl)-L-cysteine sulfoxide].5

Application

Onions can be used in virtually any meal. They can be used in meats, sauces, soups and dips and baked products.

Considerations when adding them to bread formulations:

  • Fried or powdered onions can be mixed into the dough with no significant impact on gluten development.
  • Onion rings or coarsely minced forms are usually used as toppings.
  • Given their antimicrobial activity, more yeast may be needed for proper product volume.
  • Switching from fresh to dry forms should be carried out based on total solids content, since fresh onions contain 90% water and the flavors/actives are found in the dry portion.
  • Powdered onion goes well with ground caraway and dill seeds. Rye and pumpernickel bread can be prepared using these three ingredients.
  • Crispy fried  pieces can not only add flavor, but also add a visual aspect to baked goods.

Commercially available forms of onions

Onions are sold locally in whole or fresh form. Shelf-stable forms are processed in variety of ways.  Also, the ingredient can be frozen, canned, or pickled in vinegar or brine. If they are dehydrated, the white varieties with high total soluble solids are most often used.

The following commercial forms are available for use in the baking industry:

  1. Dehydrated
  2. Freeze-dried
  3. Fried
  4. Fresh

Onions are dehydrated as flakes, coarsely minced, rings or powder. The food industry requires white onion varieties with the following attributes:1

  • Total soluble solids (>20%)
  • High degree of pungency
  • High insoluble solids
  • Low reducing to non-reducing sugars ratio to avoid caramelization
  • High crop yields
  • Good storage quality

Dehydration process using forced air

Commercial dehydration of onions is achieved by forced hot air with the process divided into several stages using different temperature profiles. In this process, the temperature conditions become milder as the moisture content falls. The process is completed by placing the dehydrated onion pieces in bins where a final moisture content of about 4% is achieved via circulation of warm air currents.1

The following steps summarize the process for dehydrating onions:1

  1. Harvesing
  2. Storing
  3. Sizing, grading
  4. Washing
  5. Peeling
  6. Slicing
  7. Drying
  8. Bin drying
  9. Screening
  10. Aspirating
  11. Grinding (for powder form)
  12. Packaging

Nutritional composition

The chemical composition of onions varies with variety, season of production and shelf life.

Macronutrients:1,2

Component g / 100 g onion (%)
Moisture 88.0–93.0
Protein 0.9–1.6
Fat Trace–0.2
Total carbohydrates 5.2–9.0
Ash 0.5–0.6
Energy 23–38 cal / 100 g

Micronutrients:1,2

Component mg / 100 g
Minerals
Calcium 190–540
Phosphorus 200–430
Potassium 80–110
Sodium 31–50
Magnesium 81–150
Sulphur 50–51
Vitamins
Vitamin D 0.3 mg / 100 g
Riboflavin 0.05 mg / 100 g
Vitamin C 0.0 mg / 100 g
Folic acid 16 µg / 100 g
Biotin 0.9 µg / 100 g
Pantotenic acid 0.14 mg / 100 g

References

  1. Lawande, K.E. “Onion.” Handbook of Herbs and Spices, 2nd edition, Woodhead Publishing Limited, 2012, pp. 417–429.
  2. Attokaran, M. “Onion.” Natural Food Flavors and Colorants, 2nd edition, John Wiley & Sons Ltd, 2017, pp. 294–297.
  3. De Rovira, D. Dictionary of Flavors, 3rd edition, John Wiley & Sons Ltd, 2017, p. 23, 214.
  4. Ziegler, H. Flavourings. Production, Composition, Applications, Regulations, WILEY-VCH Verlag GmbH & Co. KGaA, 2007, p. 237.
  5. Davidson, P.M., and Bozkurt Cekmer, H. “The Use of Natural Antimicrobials in Food: An Overview.” Handbook of Natural Antimicrobials for Food Safety and Quality, Woodhead Publishing, Elsevier Ltd., 2015, pp. 1–9.