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3.5. Insoluble matter

The average insoluble matter of honey was
0.15% for Sidr, 0.11% for Sumer and 0.10% for multiflora honey, which was below
the maximum limits of GSO standards 0.5%. 
The measurement of insoluble matter is important to detect honey
impurities higher than the permitted maximum which include wax, pollen,
honey-comb and particles of debris (IHC, 2009). This variation between samples
may be due to difference in harvesting practices and storage condition of honey
(Getu & Birhan, 2014).   Similar values reported for
Ethiopian honey, their insoluble solids ranged between 0.01 to 0.46% with a
mean value of 0.09% (Getu & Birhan, 2014).  

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3.6. Diastase

The diastase content in our samples ranged
between 1.46-18.4 schade for Sidr, 1.22-27.1 schade for Sumer and 0.78-5.55
schade for multiflora samples. According to GSO standard, diastase in honey
should be more than 3 schade, therefore, 7 samples of Sidr, 3 samples of Sumer
and 6 samples of multiflora were unconfirmed to the standard. Similar values
for diastase reported in Ethiopian honeys which averaged 13.5 schade (Getu
& Birhan, 2014), while higher level were reported in Argentina 19.7
(Cantarelli et al., 2008) also in Italy 39.1 (Esti et al., 1997). Diastase
activity is a quality factor for determining honey freshness and influenced by
botanical origin, climate of region, storage and heating (Singh & Bath,


3.7. HMF

The content of HMF in our samples ranged
between 0-3.97, 4.49-280 and 16.2-1062 mg/kg in Sidr, Sumer and Multiflora
respectively. Twelve samples of Sumer and 6 samples of multiflora were above
the GSO limit 80 mg/kg. Several Sidr samples presented no detectable HMF,
suggesting freshness and good practices by beekeepers (Marchini et al.,
2007).  Lower HMF reported for Ethiopian
honey ranged 0.5-3.2 mg/kg (Getu and Birhan, 2014) and Portuguese honey ranged
0.3-17.4 mg/kg (Soares et al., 2017). These differences could be attributed to
the variation of several factors that affect HMF formation, such as heating,
storage conditions, pH and ?oral source (Fallico et al., 2004). HMF is a
decomposition of fructose, increases with storage and prolonged heating of
honey. However these high values in Sumer and multiflora samples could be
attributed to the climatic conditions in Oman, as Sumer honey harvested in
summer with temperature could reach up to 50° C, unlike Sidr honeys which
harvested in winter. The high values of HMF indicate that the honey samples had
been heated and /or adulterated with processed sugar (Gebremariam
et al., 2014). HMF and diastase content are routinely used to evaluate honey
freshness, providing information about inadequate processing and/or
inappropriate storage conditions (Soares et al., 2017). Therefore high quality
honey should present high diastase and low HMF contents.

3.8. Proline

The amino acid proline content in our
samples averaged 449 mg/kg in Sidr, 877 mg/kg in Sumer and 487 mg/kg in
multiflora samples. Certain variability in the results, It could be attributed
to the different floral origin. Gerónimo & Fritz (2001) reported comparable
proline content in Argentine honey ranged 73 – 577 mg/kg. The proline content
is used as a criterion of honey ripeness and, in some cases, sugar
adulteration. Although no limit for proline in GSO standard, in Germany a honey
with less than 180 mg/kg is considered as either non-ripe or adulterated (IHC,


3.9. The Unconformity

Figure 1 presented the total, the passed
and the failed numbers of honey samples according to GSO standards. From the 29
Sidr samples, 10 samples were failed to GSO standards due to diastase, sucrose
and total glucose and fructose. All 21 samples of Sumer were failed due to high
acidity and HMF and to low diastase. Whereas 6 samples out of 8 multiflora
samples were failed due to low diastase and high HMF. Therefore, from the total
59 honey sample investigated in this study only 21 samples were confirmed to
GSO standards which represent 35.6%, leaving the rest of the samples which
represent 64.4% unconfirmed. Figure 2 shows the contribution percentage of each
parameter to the unconformity of all honey samples. Acidity was the highest
source of unconformity to honey samples by 30%, followed by HMF by 29%,
diastase by 25%, sucrose by 11% and total glucose and fructose by 5%.


The high acidity and HMF and low diastase
which affected all Sumer samples its mainly attributed to improper practice of
producing honey such as, harvesting time, processing techniques and storage
condition. Which lead to increase acidity by fermentation and increase HMF and
decrees diastase due to high temperature treatment and storage. The high
sucrose content in Sidr samples could be due to accidental adulterated of the
samples by feeding of bees with sucrose solution in the beehives mostly at low
forage season.


4. Conclusions

From the 58 honey samples investigated in
this study, which were produced in 18 different regions of Sultanate of Oman,
37 samples were failed to confirm to GSO standards which represent 64.4% of the
total samples. This high failure to standards, needs an effective extension
service to improve beekeepers knowledge about honey quality features and
adequate production and storage technologies. Also a better quality control of
honey market is needed to maintain consumer protection. The research on Omani
honey should be further developed, in order to understand the honey composition
and the effects of environment, climate, bee forage and production technology
on quantity and quality of honey.

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