Quality Analysis of Different Types of Honey Using Refractometer

Abstract: 

Consumption of honey and honey products has grown considerably during the last few decades. Honey is susceptible to adulteration with cheaper sweeteners. Adulteration of pure honey with synthetic honey has become much more prevalent in recent years. Physicochemical analysis is one of the methods used to measure the quality and authenticity of honey. It includes moisture content, total soluble solids and soluble sugars among others. The aims of this study are to explore the operating principle of refractometer and how it works in detecting adulteration in honey, to examine the qualities of different kinds of honey and to understand the application of food analysis instruments in analysing the qualities of food product. Refractometric method was used to determine the moisture, or conversely the soluble solids in honey which in this study, ATAGO RX-CX 5000 Series Digital Refractometer was used to determine the purity of a sample that we used which are Kelulut Honey and Processed Honey (Happy Honey) by comparing its refractive index to the value of pure substances. Through the application of digital refractometer on different types of honey, several parameters, for instances, total soluble solid, soluble sugar composition, moisture and refractive index of the honey samples could be interpreted. 

Keywords: Honey, refractometer, honey adulteration, total soluble solid, moisture, soluble sugars

1.0  Introduction

Honey is a natural sweet substance produced by bees (Apis mellifera) from the nectar of flowers or tree exudates (Liu et al, 2013). The composition of honey mainly depends on climatic and environmental conditions and the diversity of the plants from which they are harvested (Guler et al, (2007). Honey contains at least 200 substances mainly carbohydrates and water. It also contains minerals, proteins, free amino acids, enzymes, vitamins, organic acids, flavonoids, phenolic acids, and other phytochemicals (Terrab et al, 2002).  Most physical properties of honeys are defined by the concentration and composition of carbohydrates. Moisture in honey is an essential quality criterion in honey processing industries, as the probability of fermentation of honey over storage increases with moisture content (Adebiyi et al., 2004).

Consumption of honey and honey products has grown considerably during the last few decades. However, at the present time, the traceability of this food is limited to the quality of each processor’s documentation. In case of doubt or fraud, there is no standardized analysis available that can discriminate or determine the botanical (floral or vegetable) and geographical (regional or territorial) origin of the honey. Counterfeiting and product adulteration are now commonly practiced in the global food marketplace. Honey adulteration is a complex problem, which has a significant economic impact which it can be occurred by the addition of different materials (Pilizota and Tiban , 2009). Adulteration, or the addition of foreign substances to honey such as molasses, starch solution, glucose, sucrose, water and inverted sugar (Sharbt and Abdel- Fattah, 1994. Ruoff and Bogdanov, 2004. Bogdanov, 2010). Because of its high nutritional value and unique flavor, the price of natural bee honey is relatively much higher than that of other sweeteners.

 Honey is susceptible to adulteration with cheaper sweeteners. Adulteration of pure honey with synthetic honey has become much more prevalent in recent years. It should be emphasized that the adulteration of pure honey is one issue and concern about the botanical and geographical origin of honey or its authenticity is another, but the two can overlap, as in the case of adulteration by honey of other geographical origin from a country where quality measures are not as stringent and the honey price is much lower. Many foods have the potential to be deliberately adulterated, but those that are expensive and are produced under wide fluctuations in weather and harvesting conditions are particularly susceptible which honey is one such material (Pilizota and Tiban , 2009).

Physicochemical analysis is one of the methods used to measure the quality and authenticity of honey. Quality and authenticity of honey are crucial to ensure only a high quality of natural honey is offered to consumers and to avoid any health complications in the future. However, relatively few physicochemical data are available on the Malaysian honey. Physicochemical analysis is a set of tests to measure the quality and authenticity of honey. It includes moisture content, pH, free acidity, electrical conductivity, ash content, diastase, total soluble solids and soluble sugars among others (Codex Alimentarius Commission, 2001). Multiple tests needed to be conducted on a single honey sample  because  honey is  a  complex  mixture  of  various  substances  such  as  water, carbohydrates,  proteins,  enzymes,  minerals  and  microorganisms  (da  Silva et  al.,  2016). 

Refractometric method was used to determine the moisture, or conversely the soluble solids in honey as previously described by the International Honey Commission. This method is based on the principle that refractive index increases with solid content. It is also an important tool that determines the quality and grade of honey. Its accuracy has helped millions of beekeepers around the world in producing high-quality honey. The nutrient grade of the honey is measured in Brix. Higher Brix measurements mean higher nutrient grade. So in food, the higher the Brix percentage, the more nutritious the food is. It also applies in honey-making. So, the higher the Brix percentage in honey, the better the quality is.

2.0 Objectives

The objective of this experiment is to explore the operating principle of refractometer and how it works in detecting adulteration in honey. Besides, to examine the qualities of different kinds of honey, and to understand the application of food analysis instruments in analyzing the qualities of food product.

3.0  Materials and Apparatus

•          Beaker
•        Dropper
•          Tissue Paper
•     Distilled water

•          Kelulut Honey  
•   Processed Honey (Happy Honey)

•      ATAGO RX-CX 5000 Series Digital Refractometer

4.0  Methodology

1.  Several drops of distilled water were placed on the prism of refractometer.
2. ZERO button was pressed and wait for a while until "out of water" appeared on the screen.
3. Distilled water on the prism was wiped by using paper towel.
4. A several drops of kelulut honey sample were placed on the prism of refractometer.
5. START button was pressed and wait for a while until brix measurement appeared on the screen.
6. Kelulut honey on the prism was wiped by using paper towel.
7. Data appeared on the screen was recorded.
8. Testing for total soluble solid of kelulut honey was repeated 3 times.
9. All the steps were repeated for processed honey.

Here a video on how we carried out our experiment

5.0 Result and Graphic

5.1  Results

Through the application of digital refractometer on different types of honey, several parameters, for instances, total soluble solid, soluble sugar composition, moisture and refractive index of the honey samples could be interpreted. In this study, these qualities of honey were examined and could be important indicators of the occurrence of fraud or adulteration in honey, which is not uncommon in the food market nowadays.

Table 5.1.1 shows the measurement of qualities of different types of honey using refractometer

Honey types	Soluble solid (% or ˚Brix)			Moisture content (%)			Refractive Index
	1	2	3	1	2	3	1	2	3
Kelulut honey	67.6	67.6	67.9	32.4	32.4	32.1	1.4582	1.4582	1.4606
	Average = 67.7			Average = 32.3			Average = 1.459
	Std dev = 0.173			Std dev = 0.173			Std dev = 0.00139
	% error = 0.26%			% error = 0.54%			% error = 0.1%
Happy honey	78.5	76.1	78.1	21.5	23.9	21.9	1.4881	1.4806	1.4855
	Average = 77.6			Average = 22.4			Average = 1.485
	Std dev = 1.286			Std dev = 1.286			Std dev = 0.00533
	% error = 1.66%			% error = 5.74%			% error = 0.36%

5.2  Calculations

Obtaining moisture content from total soluble solid (TSS) value

                      

Kelulut honey

1^st and 2^nd trial

Moisture content = 100% - 67.6%

              = 32.4%

3^rd trial

Moisture content = 100% - 67.9%

               = 32.1%

Happy honey

1^st trial

Moisture content = 100% - 78.5%

              = 21.5%

2^nd trial

Moisture content = 100% - 76.1%

              = 23.9%

3^rd trial

Moisture content = 100% - 78.1%

              = 21.9%

Calculating standard deviation and percentage error for triplicates

 

Parameter 1 : Total soluble solid (%)


Kelulut honey

Standard deviation = 

                = 0.173

Percentage error = 0.173  x 100%

                67.7

             = 0.26%

Happy honey

Standard deviation =

   = 1.286

Percentage error = 1.286  x 100%

                77.6

             = 1.66%

Parameter 2 : Moisture content

Kelulut honey

Standard deviation = 

   

= 0.713

Percentage error = 0.173  x 100%

                32.3

              = 0.54%

Happy honey

Standard deviation = 

      = 1.286

Percentage error = 1.286  x 100%

                22.4

              = 5.74%

Parameter 3 : Refractive index

Kelulut honey

Standard deviation =

  = 0.00139

Percentage error = 0.00139  x 100%

                1.459

             = 0.10%

Happy honey

Standard deviation = 

= 0.00533

Percentage error = 0.00533  x 100%

                1.485

             = 0.36%

5.3  Graphics

Figure 5.3.1 shows the total soluble solids, or known as sugar concentration in percentage of different types of honey

Figure 5.3.2 shows the moisture content of different types of honey

Figure 5.3.3 shows the refractive index of different types of honey as derived from its brix value, as attached in the Appendix A

6.0 Discussion

6.1 Principle of Refractometer and Refractive Index

Refractometers are instruments to measure substances dissolved in water and certain oils. The refractometer works using the principle of light refraction through liquids. As light passes from air (Medium A) into a liquid (Medium B) it slows down. Whenever light changes speed as it crosses a boundary from one medium into another its direction of travel also changes, as it is refracted (Figure 1). This phenomenon is what gives a "bent" look to objects that are partially submerged in water. To put it simply, the more dissolved solids water contains, the slower light travels through it, and the more pronouced the "bending" effect on light. Refractometers use this principle to determine the amount of dissolved solids in liquids by passing light through a sample and showing the refracted angle on a scale (Mascosko, 1994).

Figure 1. Light crossing from any transparent medium into another in which it has a different speed it is refracted which is bent from its original path.

            A refractometer is used to measure the refractive index of substances, usually liquids. Most refractometers are based on the critical angle effect which defines the point of balance, the shadow point or borderline, between refraction and total internal reflection of light at a prism or sample interface (Jing Wang et al., 2018). More generally, refractometers are used to measure a Refractive Index (RI) of pure substances (liquid) as a unique characteristic, or used to measure the concentration of one substance dissolved in another. Refractive index commonly used to determine the purity of a sample by comparing its refractive index to the value of pure substances.

            The refractive index of a substance, usually given the symbol n, is a measure of the speed of light through the substance and is defined as the ratio of the speed of light in the substance to the speed of light in a vacuum. For practical purposes the speed of light in air rather than vacuum is used, the difference being very small.

Refractive Index of given substance (n)         =          Speed of light in vacuum

                                                                                                 Speed of light in substance

            Apart from the fundamental RI scale, the Brix scale is the most widely used scale on a refractometer. Brix, or sugar percetange is an internationally recognised scale, which relates the concentration of sucrose in water at 20 °C to the RI of the solution (wt/wt). Most food products are more complex than a sucrose solution which many other soluble ingredients may contribute to the overall RI. However, the Brix scale is still used as the standard. For non-sucrose based products the term ‘apparent Brix’ is strictly more correct.

            Refractometer measures total soluble solids (TSS) concentration based on the principle of refraction of light. When a ray of light travels obliquely from one medium to another, it is bent or refracted. The refraction occurs because light travels at slightly different velocities in different media, the extent being proportional to the density of the solution or the soluble solids concentration. The refractive index of a medium is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction when a ray of monochromatic light is refracted from a vacuum (air) into the medium (S.K. Mishra et al., 1989). In a Brix refiactometer, the refractive index is calibrated into degrees Brix readings.

            Total Soluble Solid (TSS) content of a solution can be determined by the refractive index. This is measure using a refractometer and is referred as the degree Brix. Brix is a term used when a refractometer equipped with scale, based on the relationship between refractive indices at 20 ֯ C and the percentage by mass of total soluble solids of a pure aqueous sucrose solution. In principle, the unit Brix, which has been in common use in industry for many years, represents the dry substance content of solutions containing mainly sucrose (Dongare et al., 2014).

6.2 Physicochemical Quality Based on Experiments Results

6.2.1 Moisture Content

The moisture content of honey (water-in-honey) is the quality aspect that determines the ability of honey to remain fresh and to avoid spoilage by yeast fermentation.  Raw honey can have a moisture content of less than 14% and the lower the water content the higher the perceived value of the honey.  It is internationally recognized that good quality honey should be processed at less than 20% moisture content (Ajlouni & Sujirapinyokul, 2010).  Low moisture content is desirable because honey may begin to ferment and lose its fresh quality if the water content is greater than 20%. 

Unpasteurized honey ferments because it contains wild yeast.  However, due to honey's high sugar concentration these yeasts are less likely to cause fermentation in honey with low water content.  The honey's low moisture content causes the yeast to enter its dormant stage preventing the fermentation process.  In honey with high moisture content the yeast is more likely to cause fermentation during storage resulting in higher acidity directly affecting the honey's quality.

Honey easily absorbs water from the air.  This means that it can be difficult to produce good quality honey with low moisture content in areas where humidity is high (Alemu et al., 2013).  Because honey's moisture content greatly affects the possibility of fermentation during storage and thus the quality of the honey, the measurement of the moisture content in honey is very important.  To control this factor, it is important that moisture content be known with a good degree of accuracy. From the results obtained, the moisture content for ‘happy’ honey (22.4 %) was lower than ‘kelulut’ honey (32.3 %). Thus, it can be identified that ‘happy’ honey was greater in the factor of storage stability and quality compared to ‘kelulut’ honey.

Honey adulteration refers to the act of adding some foreign substances into pure honey. This incident had existed since hundreds of years ago. It was recorded in “The Virtues of Honey” the first book of Sir John Hill (1957) which alerted readers: “Beware of honey with dishonest mixture or flour and other ingredients.” (Bogdanov, 2010). One of the major problem in honey adulteration is the moisture content and this had become a common problem in the market nowadays due to the difficulties in identifying the adulterated honey. Moisture is the third highest component of honey (National Honey Board, 1996). Moisture content of honey may vary from 15 to 20 % (Bogdanov, 2010). This is the main criteria used to determine the keeping quality and storage stability of honey. Besides that, the origin of honey might also relate to the moisture content of honey.

Honey from tropics might contain more moisture due to the humidity. Moisture content of honey is also closely related to its fermentation. The higher the moisture content of the honey, the higher the is possibility of fermentation happening in the honey samples. Honey that contains more than 18 % of moisture is likely to get fermented during prolonged storage (Ruoff & Bogdanov, 2004). The higher the moisture content in honey sample, the higher the survival rate of the yeast in honey. Thus, the higher the fermentation activity which occurs in honey and indirectly leads to the increase of acidity of honey.  Other than that, the moisture content of honey might also be due to the time of honey collection. Moisture content of honey that was collected during raining season is higher compared to the honey collected in the dry season.

6.2.2 Total Soluble Solids (TSS)

From the results in Table 4.1.1, it showed that average of total soluble solids (TSS) for the Trigona sp. of honey (Kelulut Honey) is 67.7 % while for Happy honey, the average of total soluble solids (TSS) is 77.6 %. However, Kelulut honey has a least percentage error of total soluble solids (TSS) which is 0.26 % compared to Happy honey which is 1.66 %. Supposedly, the standard of the total soluble solids (TSS) for the Trigona sp. of honey (Kelulut Honey) is ranged from 85.7 % to 83.6 % of TSS (Nyau et al., 2013). However, in this experiment, we only get TSS which is 67.7 % that does not comply with the standard. From the research of Tarun K. D. et al., (2016), as per Alimentarius Commision Standards (2001), a minimum TSS content of 65 % is required. Meanwhile, the standard of TSS for Happy Honey that being processed should has TSS in the range of 60% to 70% but from experiment, we get above 70% of TSS.

Total soluble solid is a measure of dissolved solids in the honey samples. This is for testing the quality of honey. The reason for testing honey for quality control purposes is to verify the authenticity of the product and to reveal the possible presence of artificial components or adulterants, as well as to address processing and market needs (Krell, 1996). This requires not only determining the total soluble solids (TSS) but also moisture and mineral content (ash), the levels of hydroxymethylfurfural (HMF), acidity, diastase activity, apparent sugars and water insoluble solids (Bogdanov et al., 1999). 

According research from Francisco Anguebes et al. (2016), the total soluble solids (TSS) can be a parameter to detect fraud in honey because the Brix ͦ scale that used in the food industry is measuring the approximate amount of sugars. The honey is mainly composed of sugars; about 25 different oligosaccharides have been detected in the composition of honey. The fructose and glucose are present in a higher concentration and provides the honey with its extreme sweetness. The total soluble solids (TSS) which are directly related to sugar content may be a reliable index of adulteration. Besides, the soluble solids are also can serve as an indicator parameter of the rate in solution solids such as sugars, organic acids and minerals, nonetheless directly related to sugars and the water levels in the samples. 

In conclusion, in this experiment, we get total soluble solids (TSS) for the Trigona sp. of honey (Kelulut Honey) is lower than Happy honey that was being processed. If all the honey samples, total soluble solids were generally more than 80 % and it can be considered of high grade and highly stable upon storage. On the other hand, honey with less than 80 % soluble solids is likely to ferment during storage. According of the grading system of the United States Department of Agriculture (USADA), honey with total soluble solids greater or equal to 81.4 % is considered to be of higher grade (A and B), while that falling between 80 % and 81.3 % is considered to be of lower grade C.

6.2.3 Soluble sugar

In this experiment, the average refractive index of kelulut honey that was 1.459 which is lower than happy honey which is have sold in market that have 1.485. The refractive index is a way to describe the speed in which light travels through a substance relative to how quickly light travels through a vacuum. The refractive index of honey can range anywhere between 1.3 to 1.7, and it is most often between 1.474 and 1.504. The results obtained were in the range. The reason why the refractive index of honey is not always the same is because of the fact that the consistency of honey can vary due to its water content. The higher the water content of honey, the lower the refractive index. This means that the higher the water content of honey, the faster lighter will travel through the honey. Dissolved sugar changes the refractive index of water substantially. The refractive index of a carbohydrate solution increase with the increases concentration. The percentages sugar, measured in degrees brix. Degrees Brix (symbol °Bx) is the sugar content of an aqueous solution. One degree Brix is 1 gram of sucrose in 100 grams (% w/w) of the solution. If the solution contains dissolved solids other than pure sucrose, then the °Bx only approximates the dissolved solid content.  

6.3 Application or other instrument in examining physicochemical properties of honey

Honey adulteration can also be detected using several modern methods such as measuring stable carbon-isotope ratios, NMR or differential calorimetry. Much attention has been paid to measuring major sugars in honey with gas chromatography (GC) and liquid chromatography coupled to various types of detectors (Abdel-Aal et al. 1993; Bogdanov et al. 2004).

Ruiz-Matute et al. (2010a) studied the sugar composition of high-fructose corn syrup (HFCS) using gas chromatography coupled with mass spectrometry (GC-MS). Sucrose syrups were analysed in parallel as a control. HFCS was shown to contain fructosyl-fructose and other unknown sugars that could be fructosyl-glucose. Honey produced using syrups for bee-feeding and was also analysed to detect the effect of these syrups on sugar composition. Fructosylfructose was detected in honey made by bees fed HFCS. Fructosyl-fructose was detected also in honey from free-flying bees and bees fed sucrose syrups, but at lower levels.

Guler et al. (2014) investigated the sensitivity of methods for the analysis of carbon isotope ratios. They analysed a total of 100 samples of unadulterated honey, honey made by bees fed with different amounts (5, 20 and 100 litres/colony) of sugar syrups. These syrups included corn syrups with high fructose-85 (HFC-85%), with moderate fructose-55 (HFC-55%), bee-feeding syrups (BFS), glucose syrups (GMS), and sucrose syrups (SS). The honey samples were analysed for their D13C values for honey sugars and proteins, the difference in the D13C values of the proteins and sugars (Dd13C) and the percentage of C4 sugars. Adulteration in honey from colonies fed syrups at 5 litres/colony was not detectable, but it was possible to detect adulteration in colonies fed 20 and 100 litres/colony of HFC-85, and 100 litres/colony of HFC-55.

Bertelli et al. (2010) published an effective method for the detection of honey adulterated using sugar syrups. It involves one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) coupled with multivariate statistical analyses. They used 63 samples of honey from various botanical sources and seven different sugar syrups marketed as specific bee-keeping products. They analysed 63 unadulterated honey samples and 63 samples of honey from colonies fed with seven different sugar syrups commonly used in adulteration of honey. The best discrimination model involved 1D-spectra and a cross verification analysis showed a prediction capacity for this model of 95.2%. The 2D NMR analyses also gave satisfactory results (cross-verification showed 90.5% accuracy).

Cordella et al. (2005) describe the development of high performance anion exchange chromatography with Pulsed Amperometric Detection (HPAEC-PAD) for the analysis of honey to detect adulteration combined with chemometric techniques for processing chromatograms for better discrimination of pure and adulterated honey. This method was investigated using honey samples containing between 10% and 40% of different industrial sugar syrups used for the feeding of honey bees.

7.0  Conclusion

In conclusion, the operating principle of refractometer and how it works in detecting adulteration in honey had been explored. A refractometer is used to measure the refractive index of substances, usually liquids. The refractometer works using the principle of light refraction through liquids. For example, refractometer measures total soluble solids (TSS) concentration based on the principle of refraction of light. When a ray of light travels obliquely from one medium to another, it is bent or refracted. The refraction occurs because light travels at slightly different velocities in different media, the extent being proportional to the density of the solution or the soluble solids concentration. Moreover, the qualities of different honey which are Kelulut Honey and Processed honey were successfully examined by test the physicochemical quality like the moisture content, total soluble solids and soluble sugars. Furthermore, the application of food analysis instruments in analyzing the qualities of food product which is the refractometer that we used in this study had been understand. The qualities of the honey we used were successfully analysed by using the refractometer.

8.0 References

1.   Abdel Aal ESM, Zeina HM, Youssef MM 1993: Aduleration of honey with high fructosecorn syrup - Detection by different methods. Food Chem 48: 209 -212

2.   Adebiyi FM, Akpan I, Obiajunwa EI, Olaniyi HB. 2004. Chemical/physical characterization of Nigerian honey. Pak. J. Nutr., 3(5), 278-281.

3.  Ajlouni S, Sujirapinyokul P. 2010. Hydroxymethylfurfuraldehyde and amylase contents in Australian honey. Food Chem., 119(3), 1000-1005. 

4.   Alemu T, Seifu E, Bezabih A. 2013. Physicochemical properties of honey produced in Sekota district, northern Ethiopia. Int. Food Res. J., 20(6), 3061-3067.

5.  Bertelli D, Lolli M, Papotti G, Bortolotti L, Serra G, Plessi M 2010: Detection of honey adulteration by sugar syrups using one-dimensional and two-dimensional high resolution nuclear magnetic resonance. J Agric Food Chem 58: 8495-8501

6.    Bogdanov. S., 2010. "Honey control. Book of honey''. chapter 9. Bee Product Science, www.bee-hexagon.net.

7.  Bogdanov S, Ruoff K, Oddo LP 2004: Physico-chemical methods for the characterisation of unifloral honeys: A review. Apidologie 35: 4-17

8.    Codex Alimentarius Commission 2001 Alinorm 41/10: Revised standard for honey, Alinorm 1 (Rome: World Health Organisation) 19-26

9.   Cordella CH, Militão JSLT, Clément MC, Drajnudel P, Cabrol-Bass D 2005: Detection and quantification of honey adulteration via direkt incorporation of sugar syrups or beefeeding: preliminary study using highperformance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and chemometrics. Anal Chim         Acta 531: 239-248

10.  Da Silva P M, Gauche C, Gonzaga L V, Costa A C O and Fett R 2016 Food Chemistry 196 309-32

11.  Dongare, M.L., Buchade, P.B., Awatade, M.N., Shaligram, A.D. (2014). Mathematical modeling and simulation of refractive index based Brix measurement system. Optik 125, 946–949.

12. Fabiola Carina Biluca et al., (2016). Physicochemical profiles, minerals and bioactive compounds of stingless bee honey (Meliponinae). Journal of Food Composition and Analysis. Volume 50; 61 – 69

13. Francisco Anguebes et al.. (2016). Application of Multivariable Analysis and FTIR-ATR Spectroscopy to the Prediction of Properties in Campeche Honey. Hindawi Publishing Corporation Journal of Analytical Methods in Chemistry Volume 2016, Article ID 5427526, 14 pages. http://dx.doi.org/10.1155/2016/5427526

14. Guler A, Kocaokutgen H, Garipoglu AV, Onder H, Ekinci D, Biyik S 2014: Detection of adulterated honey produced by honeybee (Apis mellifera L.) colonies fed withdifferent levels of commercial industrial sugar (C3 and C4 plants) syrups by the carbon isotope     ratio analysis. Food Chem 155: 155-160

15.  Guler A., Bakan A., Nisbet C., and Yavuz O., “Determination of important biochemical properties of honey to discriminate pure and adulterated honey with sucrose (Saccharum officinarum L.) syrup,” Food Chemistry, vol. 105, no. 3, pp. 1119–1125, 2007

16.  Jing Wan, Yu Lu, Zhian Lu, Weiqi Dou, Cheng Wang, and Guirong Jiang (2018). "Refractometer with broad refractive index measurement range", Proc. SPIE 10827, Sixth International Conference on Optical and Photonic Engineering (icOPEN 2018). doi: 10.1117/12.2500969.

17. Krell, R., (1996). Value-Added Products from Beekeeping. FAO Agricultural Services Bulletin No. 124, Food and Agriculture Organization of the United Nations, Rome, Italy, ISBN: 92-5-103819-8.

18.  Liu J. R,Ye Y.L, Lin T.Y, Wang Y.W, and Peng C.C., “Effect of floral sources on theantioxidant, antimicrobial, and anti-inflammatory activities of honeys in Taiwan,” Food Chemistry, vol. 139, no. 1-4, pp. 938–943, 2013.

19.  Macosko (1994). “Rheology: principles, measurements and applications”, Ed. VCH Plubishers, Inc.,United States of America.

20.  Pilizota V. and Tiban N. N., (2009). Advances in Honey Adulteration Detection. Retrieved From https://www.foodsafetymagazine.com/magazine-archive1/augustseptember-2009/advances-in-honey-adulteration-detection/

21.  Ruiz-Matute AI, Weiss M, Sammataro D, Finely J, Sanz ML 2010a: Carbohydrate compositionof high-fructose corn syrups (HFCS) used for bee feeding: Effect on honeycomposition. J Agric Food Chem 58: 7317-7322

22.  Ruoff, K. and S. Bogdanov., (2004), "Authenticity of honey and other bee products", APIACTA. 38, 317-327.

23. Sharbt, M.N.A. and S.A. Abdel- Fattah., (1994), "Honeybees production. Bulletin from technology transfer components" (In Arabic), Ministry of Agric. and Land Reclamation

24.  S. K. Mishra, P. Parasher, and P. D. Sharma (1989). Refractive index - A simple demonstration experiment. J. Chem. Educ., 66 (10), p 852.

25.  Tarun K. D. et al., (2015). Quality Evaluation of Honey from Stingless Bee (Trigon asp.) Reared by Garo Tribes in west Garo Hills of Meghalaya. J. Krishi Vegan 2015, 4(1): 91 – 94

26.  Terrab A., Díez M.J., and  Heredia F.J., “Characterisation of Moroccan unifloral honeys by their physicochemical characteristics,” Food Chemistry, vol. 79, no. 3, pp. 373–379, 2002.

27. USDA. United States Department of Agriculture. Standards for Honey Grading. USDA, Washington DC, 1985.

9.0 Acknowledgement

In performing our assignment which is quality analysis of different types of honey using refractometer, we had to take the help and guideline of some respected persons, who deserve our greatest gratitude. The completion of this assignment gives us much pleasure. We would like to show our gratitude to Dr. Siti Fatimah Zaharah binti Mohamad Fuzi, Lecturer of Food Analysis 2 (BWD20603), Universiti Tun Hussein Onn Malaysia for giving us a good guideline for assignment throughout numerous consultations. We would also like to expand our deepest gratitude to all those who have directly and indirectly guided us in writing this assignment. In addition, a thank you to Mr. Ishak bin Ayub, Assistant Science Officer, Universiti Tun Hussein Onn Malaysia who introduced us to the methodology of using refractometer. Many people especially our classmates and team members itself, have made valuable comment suggestions on this proposal which gave us an inspiration to improve our assignment. We thank all the people for their help directly and indirectly to complete our assignment.

         

Appendix A

Figure shows the table of derivation of refractive indices at 20℃ corresponding to the Brix value, as standards for honey regulated by United States Department of Agriculture (USDA).