Current Advances in Buckwheat Research (1995) : 793 - 799

114 Composition and Properties of Polish Buckwheat Honey Helena Rybak-Chmielewska and Teresa Szczesna Division of Apiculture, Institute of Pomology and Floriculture, Pulawy, Poland

Introduction The description of Polish honey is the subject of many publications which furnish detailed accounts of either one or several features of the product (Rychlik and Fedorowska 1960, Dzialoszynski and Kulik 1963, Zalewski 1966, Andrelowicz and Kotlarek 1968, Miskiewicz and Krauze 1969, Poszwinski 1972, Kraczkowska 1973, Curylo and Rybak 1973) whereas some of them deal with composition and physico-chemical properties of selected honeys. Buckwheat honey has already been the subject of a detailed study (Rychlik and Fedorowska 1965). This presentation provides a description of buckwheat honey including the changes which the product undergoes during one year of storage at a temperature of ca. 20°C.

Material and Research Methods Material Honey samples were collected from the apiary of the Apiculture Division at Pulawy. The hives were taken out to a buckwheat field in a nearby countryside.

Analytical methods Sensoric tests and methods used for the measurement of water content, reducing sugars content, and sucrose with melezitose content conformed to the procedures listed as official standards in the current Polish Norm (1988). In color determination, the standard procedure was aided by the use of a color atlas (20). Ash content was analyzed using a gravimetric method following incineration of 20 g honey samples at a temperature of ca. 500°C. Prior to incineration, samples were subjected to slow carbonization during 3 or 4 days. The results were given as means of dry matter percentages. Total acidity, free acids, lactones and pH were determined using potentiometric titration according to the method by White et al (1958). Electric conductivity was measured by Vorvohl's method (1964). The method consisted in measurements of specific conductivity of the 20% aqueous honey solution at a temperature of

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20°C. Amylase activity was detennined according to the Recommended European Standard for Honey (1970). The method is based on detennining the amount of starch hydrolyzed by uamylase present in 100 g of honey. Invertase activity was detennined polarimetrically after Hadom and Zurcher (1966). The method is based on measuring the amount of sucrose which undergoes decomposition by the enzyme in 100 g of honey under experiment conditions. Aminoacid content was detennined by the gas chromatography ofN-trifluoroacetyl-n-butylo esters after Gerke (1968). Carbohydrate content was detennined by the gas chromatography of mono-, di-and trisaccharides after Borys and Kubacki (1974).

Results Sensoric tests The color of buckwheat honey was that of dark tea (reddish brown). It corresponded to the color listed as "orange no. 19" in the color atlas (PL XVIII). The odor was very strong and resembled the fragrance of buckwheat flowers. The flavor was sweet and pungent. The crystallization was slow at 20°C and it took 2 months for the honey to solidifY. In some samples a layer of liquid honey fonned on the surface.

Chemical characteristics Water content was within 17.7 to 20.0% averaging 19.0% (Table 1). The content of reducing sugars ranged from 64.14 to 72.83%, the average being 64.46%. It rose to an average of 73.66% after one year in storage. The content of sucrose together with melezitose ranged from 0.25 to 3.06% and averaged 1.64%. After one year in storage it dropped to an average of 1.46%. Percent contents of sugars as detennined by gas chromatography are listed in Table 2. After one year in storage, there was a slight decline in the content of monosaccharides (glucose and fructose) as well as that of sucrose and a rise in the content of maltose detennined jointly with trehalose and of melibiose. It is only in honey kept in storage that small amounts of raffinose and melezitose were detected. Total acidity of buckwheat honey stayed within a range of 46.12 to 52.49, averaging 48.60 meq / kg (Table 3). When compared to other domestic honeys, buckwheat honey had the highest acidity. The provisions of the national standard "Bee Honey" ("Mi6d pszczeli") allow for a wider range of acceptable acidities (1 to 5 ml N NaOH) in buckwheat honey than in the remaining honeys (1 to 4). Other acidity-related parameters of buckwheat honey were also

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high: free acids from 38.25 to 45.50 with an average of 42.07 meqlkg, lactones from 4.80 to 8.50 with an average of 6.44 meqlkg. After one year in storage total acidity rose on average to 54.92, free acids to 46.38 and lactones to 8.63 meqlkg. Proline stood out among the gas chromatography-determined aminoacids with a content of 31.78 mg / 100 g of fresh honey which accounted for nearly a half of the total aminoacid content (Table 4) and increased even further in storage reaching 44.87 mg /100 g. Total content of free aminoacids was 72.60 mg /100 g in fresh honey to be down to 63.60 mg / 100 g after 6 months in storage. Buckwheat honey was found to be the richest in enzymes of all Polish honeys. The activity of - amylase ranged from 68.18 to 95.24 and averaged 83.18 g of starch digested by the enzyme contained in 100 g of honey. Invertase activity, expressed as grams of sucrose digested by the amount of the enzyme in 100 g of honey, ranged from 32.29 to 38.17 and averaged 34.62 (Table 5). After one year in storage, a - amylase activity declined to a half of its initial value (42.43), over the same period invertase activity was down to 30.65. Antibacterial properties of honey were estimated by the diameter of inhibition zone to the growth of a bacterial colony. The antibacterial activity was found to be highest against Staphylococcus aureus, the size of inhibition zone being 30 to 40 mm, both in fresh samples

and in stored ones (Table 6). Electric conductivity and ash content of buckwheat honey did not undergo any changes in storage, averaging 3.85 X 10-4 S cm'l and 0.257%.

Conclusions 1. Among Polish nectar honeys, buckwheat honey is outstanding for its high acidity and enzymatic activity, alongside with distinct organoleptic properties. 2. After one year in storage at ca. 200C buckwheat honey undergoes changes in the quantitative composition of sugars and aminoacids, a rise in acidity and a decrease in enzymatic activity. Ash content and electric conductivity are the only parameters unaffected by storage. 3. All parameters of fresh and stored buckwheat honey (except acidity) are within the acceptable limits as set down by the Recommended European Regional Standard for Honey.

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Table 1. Water, reducing sugars and sucrose content in buckwheat honey fresh and after one year at 20°C (%).

.

No of honey samples

water

1 2 3 4 5

19.9 19.5 17.7 17.8 20.0

71.91 69.59 72.83 68.67 64.14

0.25 1.77 0.96 2.16 3.05

19.6 19.5 17.6 17.8 19.9

77.42 75.20 77.14 70.95 67.58

0.80 0.77 1.08 1.88 2.75

Average

19.0

69.46

1.64

18.9

73.66

1.46

Fresh honey reducing sucrose sugars

water

Storaged honey reducing sucrose sugars

sucrose + melezitose.

Table 2. Percentage of sugars in buckwheat honey fresh and after six months of storage at 20°C. Sugars Fructose Glucose Saccharose Maltose + trehalose Melibiose Rafinose Melezitose

Fresh honey

Storage honey

51.60 46.59 0.27 1.26 0.28 0.0 0.0

50.52 44.06 0.24 3.72 0.78 0.05 0.63

Table 3. Acidity of buckwheat honey fresh and after one year storage at 20t (meq / kg). No of honey samples

lactone

Fresh honey total acid

1 2 3 4 5

4.87 8.49 7.37 6.99 4.50

Average

6.44

free acid

lactone

Storage honey total acid

free acid

46.74 52.49 46.12 47.64 50.00

41.87 44.00 38.25 40.75 45.50

8.00 10.52 8.12 8.00 8.50

54.00 60.50 51.00 50.60 58.40

46.50 50.00 42.80 42.60 50.00

48.60

42.07

8.63

54.92

46.38

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Table 4. Activity of invertase and diastese in buckwheat honey fresh and after one year storage at 20°C. Fresh honey -diastase

Storaged honey -diastase -invertase

No of honey samples

-.mvertase

1 2 3 4 5

35.28 38.17 33.39 32.29 34.06

68.18 88.24 83.18 81.08 95.24

26.94 36.70 30.39 26.20 33.03

38.90 50.00 38.90 38.25 46.10

Average

34.62

83.18

30.65

42.43

. grams sucrose converted per 100 g honey per hr.

.

grams starch converted per 100 g honey per hr.

Table 5. Antibacterial properties of buckwheat honey fresh and after six months of storage (diameters of stoppage growth zone of bacterium at mm). Staphylococcus aureus I IT III 42 44 36

Honey Fresh without light at 4"(; without light at 20"(; on light at 20 0 e

35 40 40

30 28 40

35 35 40

E.coli sacharoza + III I IT 20 20 20 After six months storage 15 20 20

15 20 16

16 15 15

E.coli sacharozaIT III I 16 20 19 20 20 30

I , II, III - repetition.

Table 6. Electric conductivity and ash content in fresh buckwheat honey. No of honey samples

Electric conductivity 10-4 S x cm- I

Ash %

1 2 3 4 5

3.20 3.85 3.12 4.30 4.80

0.190 0.235 0.239 0.380 0.241

Average

3.85

0.257

20 20 30

15 19 20

798 Table 7. Amino acid content in buckwheat honey fresh and after six months of storage at 20t (mg 1 100g). Amino acid

Fresh honey

Storage honey

2.59 5.22 1.23 0.90 11.08 31.78

0.64 1.54 2.70 1.46 2.97 44.87

2.08 0.99 0.09 3.84 3.03 3.84

0.43 0.83

5.35

6.30

72.00

63.60

Ala Val Gly lIe Leu Pro Thr Ser Met Hpro Phe Asp Glu

2.93 2.83 6.17

Tyr

Lys Total

Literture

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