Apple

Botanical Profile

The cultivated apple, Malus domestica, is one of the world's most important fruit crops. Fruits, peels and processing by-products are characterised by pectins, fruit acids and a diverse polyphenol profile.

Malus domestica Borkh. is a cultivated fruit tree of the Rosaceae. The cultivated apple arose through complex domestication and hybridisation processes involving Central Asian wild apples and other Malus species. Today thousands of cultivars exist with differing fruit forms, colours, aroma profiles and technological properties.

Botanically, the apple tree develops deciduous leaves, whitish to pink flowers and accessory fruits formed from the ovary and floral axis. The true botanical fruit structure is associated with the core, while the fleshy portion forms the main edible part.

The fruits are used above all. Depending on context, apple peel, dried apple pieces, press residues, apple pomace and pectin-rich fractions are also important. For botanical raw-material profiles it is important to distinguish whole fruit, peel, juice, pomace and isolated fibre or pectin fractions.

In European culture, the apple represents both an everyday fruit and a long history of cultivar breeding, storage technology and processing. Its importance lies in the combination of botanical diversity, food use and well-studied food-chemical constituents.

Phytochemistry

The phytochemical profile of apples comprises carbohydrates, organic acids, dietary fibre, polyphenols and numerous volatile aroma compounds. Pectins are particularly important as soluble fibres in cell walls and middle lamellae and play a major role in texture, gel formation and technological properties.

Typical polyphenols include chlorogenic acid, caffeic-acid derivatives, catechin, epicatechin, procyanidins, phloridzin, quercetin glycosides and other flavonoids. Distribution is not uniform: peels generally contain higher concentrations of certain flavonoids and pigments than the flesh.

The red colour of many cultivars is based on anthocyanins in the peel, while yellow and green cultivars have other pigment and aroma profiles. Cultivar, ripeness, site, storage, processing and oxidation markedly influence composition.

For extracts and botanical raw materials, polyphenol profile, pectin content, drying behaviour and browning reactions are particularly relevant. Apple raw materials can therefore have very different analytical and sensory properties depending on starting material.

Traditional Uses

The apple has been a central cultivated food plant of Eurasia for millennia. Its domestication history is frequently associated with Central Asia and trade routes between Asia and Europe. In Europe the apple developed into one of the most important fruit crops in gardens, meadow orchards and agricultural production systems.

Traditionally, apples were eaten fresh, dried, cooked, fermented or processed into purée, juice, cider, vinegar and baked goods. Apple pomace and peel also had importance in regional processing.

In European folk culture, the apple carries strong symbolism and appears in proverbs, harvest customs, monastic gardens and household traditions. This cultural role must be distinguished from modern health-related statements.

As a traditional botanical raw material, the apple is primarily a food and processing subject. Its value lies in availability, cultivar diversity, sensory breadth and its long use as a storable fruit.

Current Research

Current research on Malus domestica addresses genetics, cultivar diversity, polyphenol profiles, pectin structure, aroma compounds, storage stability and food-technological processing. An important field investigates how cultivar, cultivation, ripeness and storage influence levels of polyphenols and other constituents.

Apple peels and apple pomace are investigated as by-products of the juice and food industries. Research focuses on pectins, fibre fractions, polyphenols and possible uses in functional foods or as sustainable raw-material sources.

Nutritional studies examine apples, apple products and isolated apple constituents in different contexts. For botanical profiles, however, it is essential to distinguish whole fruit, juice, peel, pomace, pectin and specific extracts.

Research and practice show the apple to be a well-studied crop whose chemical diversity is strongly dependent on cultivar and processing. Scientific classification should therefore always identify the specific starting material.

Sources

• Kew Science: Apple – Malus domestica.
• Review literature on Malus domestica, polyphenols, pectins and apple by-products.
• Specialist literature on apple polyphenols, phloridzin, chlorogenic acid and procyanidins.
• USDA FoodData Central and food-chemistry reference data on apple fruits.
• Literature on domestication and cultivar history of the cultivated apple.