Fresh and processed wild Cantharellus cibarius L. growing in West Siberia: food value

Introduction. Cantharellus cibarius L. is a wild mushroom that has been part of human diet for many centuries. However, there is little reliable information about its nutritional value, storage conditions, shelf life, and processing. The research objective was to study the nutritional value of C. cibarius growing in West Siberia, as well as to define its storage and processing conditions. Study objects and methods. The research featured fresh and processed (boiled and salted) wild chanterelles (C. cibarius) obtained from the forests of the Novosibirsk region. The mushrooms were tested for amino acids, fatty acids, nutrients, reducing sugars, trehalose, mannit, glycogen, fiber, mucus, squalene, ash, minerals, vitamins, trypsin inhibitor, chlorides, mesophilic and facultative anaerobes, etc. The samples also underwent sensory evaluation. Results and discussion. The samples of C. cibarius proved to have a high nutritional value. The samples contained 3.6% proteins, including essential amino acids; 3.9% carbohydrates, including sugars and dietary fiber; and 0.7% lipids, including saturated, monounsaturated, and polyunsaturated acids. In addition, C. cibarius appeared to be rich in biologically active substances. It contained trypsin inhibitors that reduce the absorption of protein compounds. Purchasing centers can be recommended to use 70–80% relative air humidity. At 0–2°C, the storage time was five days; at 5–10°C – three days; at 15–20°С – two days; at 20–30°C – one day. Before processing, the mushrooms were washed twice in non-flowing water. C. cibarius also proved to be a valuable raw material for boiled and salted semi-finished products. The optimal boiling time was 5–10 min. Lightly-, medium-, and strong-salted semi-finished mushrooms were ready for consumption after the fermentation was complete, i.e. after day 15, 10, and 3, respectively. Conclusion. Boiled and salted semi-finished products from Siberian C. cibarius demonstrated excellent sensory qualities and can become part of various popular dishes.


INTRODUCTION
Mushrooms have typical taste and aroma, high nutritional value, and relatively low calorie content. As a result, they have always been an integral part of human diet. However, the advantageous properties of mushrooms depend on their chemical composition, processing method, etc. Mushrooms owe their antibacterial, anti-inflammatory, wound healing, tonic, immunomodulating, and other therapeutic properties due to various biologically active substances in their composition [1][2][3][4]. The chemical composition of mushrooms depends on the season, area, ecology, size, and age [5]. Their chemical composition includes 50-65% carbohydrates, 19-35% proteins, 2-6% fats. They are rich in palmitic, oleic, and linoleic acids, with unsaturated fatty acids prevailing over saturated acids.
Food scientists are busy developing new processing technologies to optimize mushroom production, improve the quality of mushroom products, and increase demand [7][8][9][10].
For instance, Taiwan experts studied the taste profile of canned Agaricus bisporus, Volvariella volvacea, and Flammulina velutipes. The content of soluble sugars and polyols was 22.9-30.9 μg/g in the fruiting body and 5.6-14.2 μg/g in the canning brine. Canned samples of F. velutipes appeared to have the largest amount of total free amino acids, i.e. 247 μg/g in the fruiting body and 146 μg/g in the brine, closely followed by A. bisporus (42.8 and 33.3 μg/g). V. volvacea had the lowest content of soluble sugars and polyols, i.e. 27.2 and 12.4 μg/g [11].
Some studies featured the effect of freezing and such pretreatments as blanching, soaking in water / solutions of sodium metabisulfite and/or citric acid and/ or low-methylated pectin, etc. [12]. Polish scientists proved the effect of freezing and thermal treatment on the amino acid content of A. bisporus, Boletus edulis, and Pleurotus ostreatus. Processed samples of B. edulis contained more amino acids than A. bisporus and P. ostreatus. The content of alanine, arginine, proline, cysteine, methionine, and tyrosine depended on the processing method. Limiting amino acids were detected in B. edulis, both frozen (leucine) and canned (lysine) [13].
Chinese and American scientists found that frozen, canned, and salted A. bisporus are a good source of vegetable protein (16.54-24.35 g/100 g). The content of free amino acids dropped during six months of storage, especially that of tyrosine, alanine, glutamine, and cysteine. Salting and thermal treatment led to a decrease in 5'-nucleotides [14].
Increasing the shelf life of fresh mushrooms is one of the most popular tasks of food research. Spanish scientists investigated the effect of various active substances on the shelf life of mushrooms, their color, and consumer appeal. Sodium metabisulfite in combination with citric acid and green tea extract increased the shelf life, while cinnamon essential oil and purple carrot extracts did not have enough antioxidant properties to inhibit spoilage and/or prolong the shelf life of the mushrooms [15]. Portuguese researchers proved that gamma-, electron beam, and UV irradiations increase the shelf life of fresh A. bisporus, Lentinus edodes, and P. ostreatus [16].
Scientists have always been concerned about the safety of mushroom products [17,18]. American and British researchers proposed to assess the safety of mushrooms by DNA methods, which is a promising alternative to traditional toxicological tests on animals [19].
A recent research featured five macro-and microelements in 14 species of mushrooms cultivated in China and Poland (A. bisporus, Amauroderma rude, Auricularia auricula-judae, Auricularia nigricans, Ganoderma lucidum, Lentinula edodes, Lignosus P. ostreatus, Sparassis crispa, Tremella fuciformis, Wolfiporia cocos, and V. volvacea). The samples demonstrated a high content of such toxic elements as aluminum, arsenic, and platinum. In fact, the content of platinum, nickel, erbium, and neodymium exceeded all previously published data. The quantity of the chemical elements did not make the samples toxic, but scientists will have to find a way to reduce the nickel content [20].
As a highly demanded product with high safety and quality standards, mushrooms are bound to be subject to geographical tracking by all international market members, e.g. by using the method of stable isotopes, bar coding, etc. [21,22].
Polish scientists studied the health-improving properties of polysaccharides in C. cibarius. Mushroom poly-saccharides consist of one monosaccharide in a repeating unit →6)-α-D-Manp-(1→; they inhibit COX-1 and COX-2, decrease the proliferation of colon cancer cells, and stimulate the growth of Lactobacillus [28]. Blanching appeared to decrease antioxidant activity and the content of polyphenols. When Lactobacillus plantarum was used for lactic acid fermentation of fruiting bodies, it decreased the pH value and the formation of highly concentrated single phenolic acids, e.g. gallic, homogenous, and ferulic [29]. The Polish team also studied the mineral composition of C. cibarius, which included silver, aluminum, barium, calcium, cadmium, cobalt, chromium, copper, iron, mercury, potassium, magnesium, manganese, sodium, nickel, lead, phosphorus, rubium, strontium, and zinc. The mineral profile of C. cibarius depended on the area where the mushroom was harvested [30]. A Polish-Chinese research revealed that some elements depend not only on the geographical location, but also on anthropogenic factors. For example, the Chernobyl disaster increased the cesium content in C. cibarius growing in Poland, compared to samples from Yunnan [31].
Blanching and pickling led to a 77-91% decrease in cadmium content in C. cibarius. Blanching of fresh mushrooms decreased cadmium content by 11-36%, while in frozen mushrooms it fell by about 40%. A similar rate of cadmium reduction was observed after blanching with drinking or deionized water for 5-15 min. After pickling the blanched mushrooms in diluted vinegar marinade, cadmium dropped by 37-71% [32]. Convective or freeze drying also affected the aromatic composition and sensory qualities of C. cibarius. Fresh and dried mushrooms contained 39 volatile compounds in various concentrations, the largest being 1-hexanol, 1-octene-3-ol, and 2-octene-1-ol [33,34].
Russian scientists proved that 20 min of thermal treatment detoxifies heavy metals in mushrooms [35].
Available sources reveal no information on the nutritional value of wild Russian C. cibarius, while its nutritional value is known to depend on a great number of factors, e.g. climatic zones, environmental impact, etc.
The present research objective was to study the nutritional value of wild C. cibarius growing in West Siberia, as well as the qualitative characteristics of semifinished products from C. cibarius.

STUDY OBJECTS AND METHODS
The research featured wild chanterelles (Cantharellus cibarius L.): fresh samples (≤ 4 h after mycelium separation) and processed samples (boiled and salted).
The mushrooms were young, mature, and of medium maturity. The age was defined according to the diameter and shape of the cap, the state and color of the hymenophore, and the size and condition of the stem. The mushrooms were harvested in different districts of the Novosibirsk region in 1986-2018. The batch volumes were determined according to standard procedures [5].
The species was established organoleptically [5]: the characteristics of the specimen had to meet the requirements specified in Fig. 1. The mushrooms also met the safety standards in terms of toxicity, pesticides, and radionuclides, namely the mushrooms complied with the Technical Regulation of Customs Union TR CU 021/2011 "On food safety".
The samples of C. cibarius were tested for: -total protein content using dye amide black 10В [40]; amino acid composition of proteins using an AAA-339M amino acid analyzer; total tryptophan content -by spectrophotometric method developed at the Bakh Institute of Biochemistry; qualitative analysis of proteins -by calculating the coefficient of digestibility and comparable redundancy [41]; -content of reducing sugars and trehalose was defined by the semi-micro Bertrand method [42]; mannitby the iodine-metric method [43]; glycogen -after extraction with trichloroacetic acid; hydrolysis -by the semi-micro Bertrand method [42]; cellulose -by the Pochinok method [44]; mucus -by the gravimetric method [45]; -lipid content was defined according to the Bligh and Dyer method [46]; fatty acid composition -using a Hewlett Packard gas chromatograph HP 6890 (USA); squalene -by high-performance gas-liquid chromatography in a liquid microcolumn chromatograph Milichrom A-02 (Russia); -ash content was measured by ashing the sample at 525 ± 25°С; ash weight was defined according to State Standard 25555.4-91 "Fruit and vegetable products. Methods for determination of ash and alkalinity of total ash and water-soluble ash"; -ascorbic acid was measured by the titrimetric method according to State Standard 24556-89 "Products of fruits and vegetables processing. Methods for determination of vitamin С"; thiamine, riboflavin, and niacin -by highly efficient gas-liquid chromatography in a Milichrom A-02 chromatograph according to State Standards 25999-83 "Products of fruits and vegetables processing. Methods of determination of vitamins B 1 and В 2 " and State Standards R 50479-93 "Fruit and vegetable products. Method for determination of vitamin РР (niacin) content"; -content of minerals (potassium, sodium, calcium, magnesium, phosphorus, sulfur, iron, manganese, cobalt, zinc, copper, and nickel) was described by atomic absorption in an air-acetylene flame using QUANT AFA equipment; -content of trypsin inhibitor -by the method developed by Gofman and Vaisblai [47]; -sensory properties were described according to a 100-point scale. The weighting factors for the indicators were as follows: appearance -4; color -3; consistency -7; aroma -6. Quality categories: excellent (90-100 points), very good (80-89 points), good (60-79 points), fair (40-59 points), and poor (≤ 39 points); -count of mesophilic aerobes and facultative anaerobes was measured by cultivation on nutrient media with agar according to State Standard 10444.15-94 "Food products. Methods for determination of quantity of mesophilic aerobes and facultative anaerobes"; -chloride content was determined by the argentometric method according to State Standard 26186-84 "Fruit and vegetable products, meat and meat-vegetable cans. Methods for determination of chloride content".

RESULTS AND DISCUSSION
A long-term research revealed that the chemical composition, and, consequently, the nutritional value of chanterelles (Cantharellus cibarius L.) growing in the Novosibirsk region was not affected by the climatic conditions over a number of years: the mass fraction of proteins was 3.6%; digestible carbohydrates -1.8%; mass fraction of dietary fiber -2.1%; mass fraction of lipids -0.7%; mass fraction of ash -1.2% [5].
An adult needs eight amino acids: valine, isoleucine, leucine, lysine, methionine, threonine, tryptophan, and phenylalanine. Figure 2 shows that tryptophan proved to be the limiting amino acid, while methionine + cystine appeared to be predominant.
The amino acid score can be ranked as follows: methionine + cystine (147%) > phenylalanine + tyrosine (128%) > valine (120%) > threonine (119%) > lysine (109%) > isoleucine + leucine (107%). Human body can digest 60% of the amino acids in C. cibarius due to the coefficient of digestibility and comparable redundancy. The coefficient of digestibility of the amino acid composition of the protein (0.607 CU) reflects the balance of essential amino acids in relation to the standard [41]. The indicator of comparable redundancy (22.2%) describes the total amount of unused amino acids in an amount equivalent to their potentially digestible content in 100 g of the reference protein [41]. Therefore, C. cibarius is a potential source of methionine, phenylalanine, valine, and threonine. The amino acids are responsible for the specific aroma and taste: methionine, phenylalanine, tyrosine, valine, isoleucine, and leucine add bitterness while threonine adds sweetness [48].
The qualitative composition of carbohydrates in C. cibarius is highly variable [49]. The carbohydrate composition of C. cibarius is represented by 1.5% mono-(glucose) and oligosaccharides (trehalose), Thick, with branching veins, forked, descending to the s the same color as the cap (turns brown after processin Conical, almost cylindrical below the gills, tapering down Firm, rubbery; white-yellow (turns brown after processi fresh mushrooms have a sharp taste that disappears after b White In C. cibarius 0.3% polyols (mannit), 0.1% glycogen, 2% fiber, and 0.8% mucus. Mono-and oligosaccharides, as well as polyols, are responsible for the typical taste of C. cibarius. This mushroom owes its physiological value due to trehalose. It consists of two molecules of D-glucose, mannit, glycogen, insoluble fiber, and soluble mucus. Trehalose and mannitol perform mainly a protective function in stress-induced situations. Glycogen performs the accumulative function; for example, it stores energy, which, if necessary, replenishes the lack of glucose. Insoluble fiber and branched sulfated arabinoxylans perform the protective function as they bind and remove toxic and radioactive elements.
The research revealed that 100 g of C. cibarius contained about 3.6 g of lipids. Lipids define sensory properties of fresh and processed products and also determine their stability during storage. Figure 3 demonstrates that the lipids of C. cibarius include fatty acids with 14-24 carbon atoms in the carbon chain.
The fresh samples contained a significant amount of vital biologically active substances, such as vitamins, macro-and microelements, etc. [51].
Micro The samples also demonstrated a trypsin inhibitor in the amount of 0.44-0.67 mg/g, which blocks the activity of enzymes in the digestive tract and also reduces the absorption of protein compounds.
Fresh mushrooms are conditionally-live products because of the ongoing irreversible biological and biochemical processes as they consist mainly of water   Thick, with branching veins, forked, descending to the stalk; the same color as the cap (turns brown after processing) Conical, almost cylindrical below the gills, tapering downwards Firm, rubbery; white-yellow (turns brown after processing); fresh mushrooms have a sharp taste that disappears after boiling White min (about 89.1%), proteins, and carbohydrates. High temperature, relative humidity, and long-term storage spoil the sensory properties of mushrooms, release cell juice, etc. As a result, scientists have to define shelf life for each type of mushroom, before processing under controlled and unregulated conditions. Table 1 shows the results of sensory evaluation of C. cibarius after 72 h of storage under different conditions.
When harvested, the mushrooms were fresh, undamaged, with well-developed hymnephors, uniform in size, and the number of stems matched the number of caps. After a while, some specimen became slightly wilted and/or crushed. After longer storage, the wilting increased, as did the number of crashed specimen. Eventually, all the mushrooms become wilted and slimy and demonstrated signs of tissue maceration.
The uniform yellow color of the fresh mushrooms gradually became heterogeneous and then browned slightly. The browning became more and more pronounced over time. The initial consistency was firm but gradually turned semi-firm and soft. The smell of the fresh mushrooms was typical for C. cibarius and pronounced; over time, the smell began to disappear and became weakly expressed, insignificant, musty, and even putrid.
Fresh mushrooms are hardly ever consumed raw. As a rule, they are served only after processing. Washing is the first procedure to prepare raw materials for processing. It removes impurities and microorganisms. Double washing in non-flowing water proved optimal for C. cibarius (Table 2).
Boiling in salt water is one of the processing methods for C. cibarius. The concentration of food salt in the finished product was 2.0-3.0%. After 5-10 min of boiling, the mushrooms maintained their typical color and aroma but did not retain the required tough-elastic consistency (Table 3). When the boiling time exceeded 15 min, the mushrooms developed atypical rubbery consistency, smell, and browning.

Figure 6
Basic nutrients in the semi-finished product from Cantharellus cibarius, depending on the sodium chloride content, % from the brine at 10 ± 5°C made it possible to obtain ready-to-use lightly-salted or medium-salted products after 10-15 days. Strong-salted mushrooms needed 3-4 days at 25 ± 5°C with two or three replacements of brine. As a result of diffusion processes, the semifinished products lost some amount of water-soluble substances (Fig. 6). The concentration of sodium chloride affected the amount of free amino acids, saturated and monounsaturated fatty acids, riboflavin, nicotinic acid, and nicotinamide, which dropped to 25.0, 18.5, 50.8, 37.5, 3.7 and 19.8%, respectively. The proportion of polyunsaturated fatty acids reached 20.3%.
Lightly-and medium-salted semi-finished products retained their quality characteristics for six months of storage at ≤ 25°C and a relative humidity of ≤ 75% in the dark in hermetically sealed glass jars. Strong-salted mushrooms retained their quality for 12 months under the same conditions.
At the beginning of storage, the salted semi-finished products had microbial count of 2.6×10 3 to 4.5×10 3 , e.g. micrococci, spore bacteria and bacteria without spores, and yeast. The number of microorganisms gradually increased, especially that of yeasts and molds, which caused a sour and/or musty odor, softening, whitish or green coating, etc. The number of thermophilic bacteria with spores of the Clostridium butyricum kind, which caused a putrid odor and gas release.
During storage, the protein content in the salted semi-finished products decreased gradually under the effect of hay bacillus, mold, and butyric acid bacteria. The hydrolytic breakdown of protein increased the amount of free amino acids by 25-30% of the initial content.
The content of saturated and monounsaturated fatty acids increased by an average of 21 and 142%,  respectively, while the amount of polyunsaturated acids decreased by 34%. These changes resulted from oxidative and hydrolytic processes, e.g. under the effect of mold and butyric acid bacteria, which were responsible for the typical mushroom smell. By the end of the shelf life, the salted semi-finished products had almost no riboflavin left, and the amount of niacin dropped by 50%. No trypsin-inhibiting activity was detected in the canned samples.

CONCLUSION
In the Novosibirsk Region of West Siberia, chanterelles (Cantharellus cibarius L.) are still harvested in the wild, and no efforts are being made for their industrial cultivation. C. cibarius proved to be a good source of such nutrients as proteins, carbohydrates, lipids, vitamins, macro-and microelements, etc. The mushrooms contained a significant amount of amino acids, e.g. methionine, phenylalanine, valine, threonine, etc., squalene, trypsin inhibitors, and other bioactive substances.
The sensory evaluation revealed the optimal storage time for C. cibarius in marketing centers, depending on the temperature. The microbiological tests showed that C. cibarius has to be double-washed in non-flowing water before processing. The sensory evaluation showed that boiled lightly-, medium-, and strong-salted semifinished products from C. cibarius should be consumed within 15, 10, and 3 days after the end of fermentation, respectively. Further research into the nutritional value of fresh and processed C. cibarius can improve the quality of mushroom products.