Essential oil , highly volatile substance isolated by a physical process from an odoriferous plant of a single botanical species. The oil bears the name of the plant from which it is derived; for example, rose oil or peppermint oil. Such oils were called essential because they were thought to represent the very essence of odour and flavour. Distillation is the most common method for isolation of essential oils, but other processes—including enfleurage extraction by using fat , maceration, solvent extraction, and mechanical pressing—are used for certain products. Younger plants produce more oil than older ones, but old plants are richer in more resinous and darker oils because of the continuing evaporation of the lighter fractions of the oil. Out of the vast number of plant species, essential oils have been well characterized and identified from only a few thousand plants.
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Aroma compoundVIDEO ON THE TOPIC: Silicon Valley Start-up Digitizes Aroma and Taste for Medical, Manufacturing and Food Production
Plant breeders have made considerable advances producing cultivars with higher yields, resistant to pests and diseases, or with high nutritional quality, without paying enough attention to flavour quality.
Indeed, consumers have the perception that fruit aromas and flavours have declined in the last years. Attention is given nowadays not only to flavoured compounds but also to compounds with antioxidant activity such as phenolic compounds. Fruit flavour is a combination of aroma and taste sensations. Conjugation of sugars, acids, phenolics, and hundreds of volatile compounds contribute to the fruit flavour.
However, flavour and aroma depend on the variety, edaphoclimatic conditions, agronomical practices and postharvest handling. This chapter reviews the aromas and flavours of the most important fruits and discusses the most recent advances in the genomics, biochemistry and biotechnology of aromas and flavours.
Generation of Aromas and Flavours. Quality in horticulture can be defined as the traits of a given commodity, regardless of its yield [ 1 ]. Here, we not only include visual appearance, ability to endure postharvest processing but also chemical and nutritional composition and flavour. Great advances have been made in horticultural breeding, obtaining fruits with characteristics that are those that growers e.
In parallel to this increase in breeding, knowledge regarding chemical composition and flavour traits has too been rising, also followed by insights on physiological, metabolic and biochemical pathways taking place in plants. However, increasing flavour of fruits by breeding is still not an easy task, due to the multitude of factors affecting the compounds responsible for this characteristic, like climate, production systems and pre- and postharvest processing [ 3 ]. The aroma fraction of flavour can even influence the perception of other traits, as recorded for sweetness and sourness [ 5 ].
Knowing the preferences of consumers and aiming to fulfil those expectations regarding the flavour of fruits, besides increasing the probability of producers to easily sell their commodities, they will also be linked to an expected improvement in nutritional uptake, as better-tasting fruits will likely replace less healthy snack foods [ 1 ]. New tools, namely those related to molecular techniques, allow the identification of genes responsible for biosynthesis of compounds and open new perspectives for the improvement of flavour, by cloning those genes, increasing that specific pathway or silencing the expression of a gene responsible for an undesired compound [ 2 ].
In this chapter, we will review the aroma and flavour compounds of the major fruits fresh fruits and nuts and, finally, review the latest advances in genomics, biochemistry and biotechnology of aromas and flavour compounds.
Volatile compounds are produced as indicators of fruit ripening, and they can be classified as primary present in intact tissues or secondary compounds result of tissue disruption [ 7 ]. Different fruits produce different volatile compounds, although their precursors are phytonutrients and the resulting volatile compounds are usually esters, alcohols, aldehydes, ketones, lactones and terpenoids [ 8 ]. Furthermore, they can lead to modifications in the pathways involved in volatile biosynthesis.
Volatiles with critical importance in aroma and flavour characteristics are biosynthesized from amino acids, lipids and carbohydrates, via a limited number of major biochemical pathways [ 9 ]. The first limiting step for volatile formation is the availability of primary precursors, including fatty acids and amino acids, compounds highly regulated during fruit development in terms of amount and composition [ 10 ].
Some of the fruits with a higher amount of production and more commonly consumed worldwide are apples, bananas, cherries, oranges and grapes, which are shortly addressed here. In apples, over volatile compounds were described [ 12 ], although they can be considered cultivar specific [ 13 ] and maturation dependent, from aldehydes to alcohols and esters [ 14 ].
The latter chemical class is predominant in ripe apples, and straight and branched esters can be found, namely ethyl, butyl and hexyl acetates, butanoates and hexanoates [ 15 ]. There is a clear increase of volatile compound production in apple skin, rather than in the internal tissues, due to a higher abundance of fatty acid substrates or increased metabolic activity [ 16 ].
The relative amount of each compound is, as referred earlier, linked to a specific cultivar and cannot only be used for cultivar discrimination but also to monitor ripening of fruits [ 17 ]. In apples, branched chain esters are produced from the breakdown of leucine, isoleucine and valine, while straight chain esters are synthesised from membrane lipids [ 18 ]. The hydroperoxides that result from these reactions are converted to aldehydes, then to alcohols and finally to esters.
For banana, about volatile compounds have been described, although the really odorant are less than 40 [ 20 ]. Major volatile compounds that contribute to banana aroma are volatile esters, such as isoamyl acetate and isobutyl acetate [ 22 ] but also isoamyl alcohol, butyl acetate and elemicine [ 23 ].
As for other fruits, the ripening process changes the volatile profile, with increased concentration of acetates and butanoates [ 24 ] and is cultivar dependent [ 25 ]. For cherries, over volatile compounds have been identified, including free and glycosidically volatile compounds, belonging to the chemical classes of carbonyls, alcohols, acids, esters, terpenes and norisoprenoids [ 27 ].
Some ketones have also been found in cherries, although they have relatively low importance in overall aroma [ 28 ], while alcohols, being the most abundant benzyl alcohol, 1-hexanol and E hexenol, are responsible for green notes and the fresh green odour.
The content of esters in cherries increases during ripening, but their relative abundance is low. Terpenoid compounds are also present in cherries at low levels, limonene, linalool and geranylacetone being the most common [ 30 ]. However, these compounds, although representing the large majority of the volatiles, are not the ones more responsible for the aroma, as their contribution is limited due of high odour-detection thresholds.
Most of the grape cultivars have no scent, although the wines obtained from them are full of aromas [ 33 , 34 ]. A great number of compounds have been recorded, including monoterpenes, C13 norisoprenoids, alcohols, esters and carbonyls [ 35 , 36 ]. If linalool and geraniol have been identified as major aroma compounds in both red and white grapes [ 37 ], the volatile profile can be useful for the discrimination of grape cultivars [ 36 ].
Major free volatile compounds are hexanal, E hexenal [ 36 ] while glycosidically bound include terpene and benzenic glycosides [ 34 ].
Other monoterpenes that can also add to Muscat aroma were rose oxide, citral, geraniol, nerol and citronellol [ 38 ]. Although the flavour of fruits is the interaction of taste and aroma, the chemical composition of fruits organic acids, sugars, amino acids, pro-vitamins, minerals and salts can also influence aroma perception and ultimately, flavour. However, this relationship is not completely understood, as measurement of sugars as soluble solids, in orange, does correlate to sweetness but in mango does not [ 4 ].
The main organic acids in fruits are malic, citric and tartaric, citric being the most sour and tartaric the least [ 40 ]. Citric acid is linked to citrus fruits, tartaric to grapes and malic to apples, and they are responsible for the sour flavour detected on those fruits. Other fruits, like melon or banana, have reduced acidity [ 41 ]. The presence of minerals and salts can change the perception of acidity, by combining with organic acids, influencing the buffering capacity [ 40 ].
Many research studies on the flavour of fruits give us a good overview of this particular trait of these commodities. However, much is still to be done, since many cultivars are yet still less studied. Furthermore, the link between taste and aroma compounds and the consumer perception of those is still not well understood, and this should be the ultimately goal to achieve consumer-oriented commodities.
Global consumption of nuts grew in the last years and it is expected to grow continuously on a yearly basis [ 48 ]. In , almonds, cashews, walnuts and hazelnuts were the most preferred nuts by the consumers [ 49 ] but other nuts, such as pine nuts, pecans, chestnuts, Brazil nuts, macadamias and pistachios, are also an appreciated food, especially in the regions where they are regularly produced.
They are generally consumed as whole nuts fresh, roasted or salted or used in a variety of commercial products and processed food [ 50 ]. Nuts have been a regular part of the human diet since pre-agricultural times [ 51 ] due to their nutritional value, sensory properties [ 49 ] and potential health properties [ 50 , 52 ], and their consumption can reduce cardiovascular disease risk, the incidence of cancer and type 2 diabetes mellitus [ 53 ], as well as obesity and ageing effects [ 54 ].
Nut quality related to consumer purchase decisions is based on nut appearance such as size, colour, cleanness and freedom from decay and defects [ 55 ] but textural properties [ 54 , 56 ] such as aroma and flavour also play an important role in consumer acceptability [ 57 ]. Sweetness, oiliness and roasted flavour are commonly associated with good overall nut sensory attributes [ 55 ], some compounds generated during the roasting process responsible for the typical nut flavour [ 58 ].
Roasting is a common practice used by the nut industry and involves several physical-chemical processes [ 59 ], which can modify the odour, flavour and quality of the final product [ 60 ], including negative effects, such as rancidity [ 61 ]. In general, nuts are characterised by their high content in unsaturated fatty acids [ 49 , 50 , 57 ] which make them highly sensitive to oxidation during the roasting process leading to the formation of harmful free radicals [ 61 ], which are responsible for undesirable odours and flavours [ 62 ].
As a result, the roasting process negatively affects the nutritional quality of nuts but also may influence both the formation of health-promoting components and those with potentially adverse health effects [ 63 ]. So, selecting the appropriate roasting conditions, mainly temperature and time, is crucial for achieving higher nut quality [ 55 ], which is also dependent on the genotype. In comparison, the compounds that indicated oxidation only increased by 1.
Nevertheless, as it occurs with other foods, the characteristic flavour of nuts is dependent on the volatile compounds. During roasting and other heat processes, additional volatile compounds are formed from reactions among food compounds. In roasted nuts, a wide range of volatiles contribute to the typical and desirable roast flavour.
The benzaldehyde was the predominant volatile compound present in the raw samples and is associated with a marzipan-like flavour [ 64 ]. Many of these compounds are typically generated during the complex and well-known Maillard non-enzymatic browning reaction that occurs during roasting. Volatile compounds like pyrazines, furans and pyrroles have been previously identified as key compounds of roasted almond aroma and concentration of many of these volatile compounds increased with roasting time [ 64 ].
In a research conducted by Clark and Nursten [ 66 ], over aroma compounds were identified as having nutty aromas. This work indicated benzaldehyde, 3,4-methylenedioxybenzaldehyde and 4-methylbenzaldehyde as responsible for nutty aromas in almonds, while 2,4-octadienal and 4-pheynylpentenal were linked to the same attribute in walnuts and 2-ethylmethylpyrazine in roasted peanuts. In the harvest year, edaphoclimatic conditions of orchards and storage conditions have also been mentioned as key factors determining overall nut quality.
Grapes belong to the large group of fleshy fruits [ 67 ]. Therefore, grape flavour depends on the content and composition of several groups of compounds [ 81 ]. Among the compounds responsible for the aromatic quality are monoterpenes and C 13 -norisoprenoids. These compounds are indigenous from the grape and responsible for intense fruity and floral attributes in wines, contributing to the wine varietal aroma [ 82 , 83 , 84 ]. The aroma compounds, which are secondary metabolites of the plant metabolism, are distributed between the pulp and skin of the grape berry, with the highest concentration in the grape skin [ 92 , 93 ].
Vitis labrusca and Vitis rotundifolia cultivars have a distinct and pronounced odour; the foxy aroma of V. Chemical compounds originated from several sources contribute to wine aroma. Grape volatile aroma compounds, such as monoterpenes, C 13 -norisoprenoids, methoxypyrazines and thiols, if present, are of major importance for the wine varietal character [ 96 ].
The volatile compounds found in wine presented different sensory attributes like fruits such as cherry, pear or passion fruit [ 97 ]. As already mentioned, the flavour of fruits is a complex set of interactions between two main sensations: taste and aroma [ 2 ].
Taste is mainly a set of sweet and sour sensations linked to the presence of sugars and organic acids although other minor compounds affect bitterness, astringency or saltiness. However, the aroma is usually the predominant sensation, surpassing taste [ 98 ]. Indeed, if taste sensations, detected in mouth, are recognised by six classes of receptors sweet, sour, salty, bitter, umami and fat-taste , for flavour complexity, where the olfactory system is essential, olfactory receptor genes are known in humans [ 1 ].
The known decrease in flavour of fruits is strongly connected to the pressure on the producers: they are usually paid depending on physical characteristics of fruits size, shape and colour but not to chemical traits, so the selection of cultivars is performed to enhance those qualities; the ripening of fruits is delayed as much as possible to make sure that they are able to withstand harvest, handling, storage and shipping without damages, but without a normal ripening, flavour sensations decreased [ 99 ].
Considering that flavour perception relies on the interaction of a considerable amount of compounds, it makes it one of the most challenging quality attributes to manipulate, which has led to a reduced attention given to this theme [ 40 ]. To achieve the goal of horticultural commodities of full flavour, some strategies can be followed, including changes in agricultural practices but also genetics tools, using the information on the known pathways of formation of those compounds linked to taste and aroma.
Considering the first approach, one should cite the preharvest factors such as genome or growing conditions, harvest maturity or postharvest storage like those important in the final flavour of any horticultural commodity [ 40 ].
Some of them are somewhat easy to control growers are able to choose the cultivar, cultural practices and postharvest procedures , while others, such as climate conditions, are outside human influence.
The choice of the cultivar to grow and its link to flavour and how chemical components in the plant tissue are expressed are connected to genetic backgrounds [ 99 ]. Indeed, recent works comparing cultivars of sweet cherry [ ], peach [ ], gooseberry [ ], fig [ ] or pear [ ], to cite a few, show how genetic backgrounds can influence chemical composition and ultimately flavour, recognised by sensory evaluation.
Included in those preharvest factors are weather, soil preparation and cultivation, soil type, irrigation, fertilisation practices and crop loads, while for postharvest, it should be mentioned that storage temperature management, packaging under controlled or modified atmosphere, the use of edible coating, heat or physicochemical treatments are the factors [ ].
The next step on flavour research was given when information on biosynthesis was obtained by using molecular and biochemical approaches. Knowing the metabolic pathways, namely the genes involved and the associated enzymes but also the regulatory elements hormones and transcription factors or which mechanisms are implicated in the storage or sequestration of volatile precursors, is key in allowing a biotechnological approach to their manipulation [ ].
The genes that are linked to flavour can be mostly divided into two categories: those encoding for enzymes and those responsible for factors regulating pathway output [ 1 ]. If the knowledge for synthesis pathways and genes for those enzymes responsible has been increasing rapidly, the regulation of metabolic pathway output is not well understood, and the number of genes involved may be quite large, as found for strawberry, where 70 quantitative trait loci QTLs affecting volatiles and their precursors have been identified [ ] or mandarin QTLs [ ], for instance.
As referred earlier, the compounds responsible for aroma can be divided in several classes, the most important being monoterpenes, sesquiterpenes, lipids-, sugars- and amino acid-derived compounds. Knowing how they are biosynthesized and what is involved, when and how are key steps to allow their manipulation. The large part of the available research on the manipulation of flavour has been conducted on tomato, as it is a plant easy to transform, with an associated high economic importance [ ] and information regarding this fruit is readily available e.
Essential oils are fragrant, volatile substances, which different plants parts, essentially flowers, leaves, fruits, roots, may contain. They are lightly distillated with a vapor from raw plant material. The essential oils have a wide range of cosmetic and medical actions due to the presence of up to complex organic compounds with different chemical structure in their composition. The properties of essential oils are apparent by their complex pharmacological, biochemical and clinical effects due to their action on three levels: molecular, psychoemotional, and on the level of nervous system - because every smell has several chemical substances.
Metrics details. Metabolic engineering has been enabling development of high performance microbial strains for the efficient production of natural and non-natural compounds from renewable non-food biomass. Even though microbial production of various chemicals has successfully been conducted and commercialized, there are still numerous chemicals and materials that await their efficient bio-based production. Aromatic chemicals, which are typically derived from benzene, toluene and xylene in petroleum industry, have been used in large amounts in various industries.
BUTTER AND DAIRY SPREADS
While most fragrance chemicals are not disclosed, we do know that some are linked to serious health problems such as cancer, reproductive and developmental toxicity, allergies and sensitivities. Clearly, there is a need for stronger regulations, more research, and greater transparency. Fragrance is defined by the FDA as a combination of chemicals that gives each perfume or cologne including those used in other products its distinct scent. Fragrance ingredients may be derived from petroleum or natural raw materials. Companies that manufacture perfume or cologne purchase fragrance mixtures from fragrance houses companies that specialize in developing fragrances to develop their own proprietary blends. These additives are frequently, but not always, listed on product labels.SEE VIDEO BY TOPIC: SUGAR - How It's Made
These guidelines are intended to provide a broad framework permitting the development of more specific group or individual standards, according to the requirements of individual countries. Fat spread: A fat spread is a food in the form of an emulsion mainly of the water-in-oil type , comprising principally an aqueous phase and edible fats and oils. Edible fats and oils: Foodstuffs mainly composed of triglycerides of fatty acids. They are of vegetable, animal, milk or marine origin. Tables Restricted zone s may be imposed, with respect to the fat content and to the proportion of milk fat to other types of fat, in accordance with national or other relevant legislation. Concerning the fat content, the IDF standard states that fat spreads shall be classified into three groups, according to the origin of the fat. The name of the food shall be as specified in national legislation.
An aroma compound , also known as an odorant , aroma , fragrance , or flavor , is a chemical compound that has a smell or odor. For a chemical compound to have a smell or odor it must be sufficiently volatile to be transported to the olfactory system in the upper part of the nose. Generally molecules meeting this specification have molecular weights of less than Flavors tend to be naturally occurring, and fragrances tend to be synthetic.
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Castor oil as a potential renewable resource for the production of functional materials
Plant breeders have made considerable advances producing cultivars with higher yields, resistant to pests and diseases, or with high nutritional quality, without paying enough attention to flavour quality. Indeed, consumers have the perception that fruit aromas and flavours have declined in the last years. Attention is given nowadays not only to flavoured compounds but also to compounds with antioxidant activity such as phenolic compounds. Fruit flavour is a combination of aroma and taste sensations. Conjugation of sugars, acids, phenolics, and hundreds of volatile compounds contribute to the fruit flavour. However, flavour and aroma depend on the variety, edaphoclimatic conditions, agronomical practices and postharvest handling. This chapter reviews the aromas and flavours of the most important fruits and discusses the most recent advances in the genomics, biochemistry and biotechnology of aromas and flavours.
Metabolic engineering of microorganisms for production of aromatic compounds
Plants provide us with an enormous array of chemicals essential to industry and to our daily lives. But why are the chemicals there and why does the plant produce them? Please be aware that the information provided on this page may be out of date, or otherwise inaccurate due to the passage of time. For more detail, see our Archive and Deletion Policy. In their poisons, antibiotic agents, prickles and foul tastes, they developed defences against attack long before human stockades and pesticides. Many of the chemicals produced by plants are linked to the ingenious strategies that plants have developed to help them flourish and survive. Some of their defences include the thick, insulating bark of many trees, and the vicious thorns on roses. But what is it that makes the stem hairs on stinging nettles produce a rash.
Aromas and Flavours of Fruits
Castor oil is increasingly becoming an important bio-based raw material for industrial applications. The oil is non-edible and can be extracted from castor seeds from the castor plant belonging to the family Euphorbiaceae.
Hui , E. Progress in the biological and microbiological sciences involved in the manufacture of these foods has led to commercialization and heightened interest among scientists and food processors. Handbook of Plant-Based Fermented Food and Beverage Technology, Second Edition is an up-to-date reference exploring the history, microorganisms, quality assurance, and manufacture of fermented food products derived from plant sources. The book begins by describing fermented food flavors, manufacturing, and biopreservation.
Может быть, он разломился надвое еще в космосе, и эта часть рухнула. Ответ стал понятен лишь после того, как они вновь отправили робота на разведку и сами обследовали все.
Никаких сомнений не оставалось, когда Элвин обнаружил на холмике близ корабля ряд пологих насыпей, каждая метра в три - Так, значит, они сели здесь, - размышлял Хилвар, - и проигнорировали предупреждение. Они были любопытны.
И потом -- зачем им все эти хлопоты, зачем, спрашивается, было зарываться в землю при все еще доступном небе. Возможно, это Пришельцы не разрешали им летать, хотя мне и трудно в это поверить. Или, может быть, все это было сооружено в переходный период, когда люди еще позволяли себе путешествовать, но уже не хотели, чтобы хоть что-то напоминало им о космосе.