Development of a Date Confectionery: Part 1. Relating Formulation to Instrumental Texture

Abstract

The Sultanate of Oman in the Middle East produces a large amount of dates, which in 2003 amounted to about 285,360 tons. Most of the harvest is used for animal feed and the rest for local consumption. The need to utilize dates in a more efficient way is a must. In this study, a new candy was developed using two date varieties, i.e., Khalas and Umesilla thus spanning from top to bottom of the quality range in terms of consumer preference. Proximate analysis argues that products are nutritious and can contribute especially to the daily allowance in macro-elements. Texture profile analysis suggests that the affordable date candy of Umesilla belongs to the same family of products with the Khalas candy in terms of the attributes of hardness, firmness, brittleness and adhesiveness. Products were aged up to thirteen weeks, with results demonstrating that the textural quality remains stable throughout the storage period.

Keywords:

• Dates
• Paste
• Candy
• Texture Profile Analysis

INTRODUCTION

Date palm (Phoenix dactylifera) is a perennial monocot plant belonging to the plant family Palmaceae.[1] The tree is one of the oldest plants dating back perhaps 30–70 million years. There are around 8 million date palms cultivated in 84.5 thousand acres in the Sultanate of Oman with an annual production of over 285,360 tons of dry dates.[2] Less than 10,000 tons are exported annually.

Dates are divided into two major categories depending on their use: table dates and processing dates. The former include varieties that are favored by humans, i.e. Dhahra Khalas, Abu Narinja, etc. The latter include varieties which are not desirable for human consumption thus being left for animal feed or they undergo limited processing, i.e., Mabsly, Um Essilah, etc.[2] Table and processing dates are about 64 and 36% of the total palm-tree population, respectively. Furthermore, the average yield per date palm tree is 45.3 and 43.6 kg for table and processing dates.[3]

Dates are well known for their nutritional value comprising sugars, dietary fiber, protein, polyphenolic compounds and ash. The dietary fiber components include cellulose, pectic substances and hemicellulose.[4,5] Eight vitamins (A, B1, B2, B6, C, niacin, folic acid, and pantothenic acid) and thirteen minerals (chlorine, sodium, potassium, calcium, magnesium, zinc, copper, phosphorus, manganese, cobalt, selenium, barium, and iron) can be found in dates.[6] The chemical composition varies depending on the variety, region of cultivation, processing, fertilization, pollination type, etc. For example, Khalas consists of 62% sugar and 15–17% moisture whereas Umesilla consists of 70% sugar and 11–14% moisture [7].

Through the years, research in the textural properties of food materials developed a protocol that identified certain parameters used to control quality. A school of thought argues that these can be divided into the primary characteristics of firmness, hardness, fracturability (brittleness) and adhesiveness, and the secondary (or derived) properties of springiness and cohesiveness.[8] Texture Profile Analysis (TPA) has been utilized widely by academics and industrialists to record and manipulate the structural behavior of processed foodstuffs in order to improve their quality.[9]

There is no published work on the texture and sensory of industrial formulations containing dates as the main ingredient. Early data describe the viscosity, physicochemical and structural properties of liquid date concentrates and unprocessed raw dates.[10–15] The aim of the present communication (part 1) is to formulate a novel and nutritious date confectionery (candy) using dry dates (Arabic tamar). The chemical composition of the product was evaluated and discussed in connection to its rheological properties. In part 2 of this work, a relationship is developed between the instrumentally derived textural characteristics and the sensory profile obtained using a trained taste panel.

EXPERIMENTAL

Formulation of the Date Candy

Two Omani date cultivars were used in the dry form, namely: Khalas and Umesilla. The drupes were obtained from local farmers (Batinah region) and from the agricultural experimental station of Sultan Qaboos University. Nuts and flavorings were purchased from the local market.

Candies were prepared as follows: Dry dates were pitted and made into a paste using water and rose water (stage 1). This was followed by addition and thorough mixing of melted butter (stage 2). Powdered toasted pistachios, cashew nuts and almonds were incorporated in the formulation. Finally, coconut, cardamon and cinnamon powder were included in the mixture. The paste was then made into balls of 2 cm in diameter each. These were rolled in coconut powder (stage 3).

The three stages were analyzed separately in order to facilitate understanding of the effect of ingredients on the textural profile. Some preparations were further treated by cooking on low heat at 50° C for 5 minutes. Thus, four different candies were made (uncooked/cooked Khalas and uncooked/cooked Umesilla) and for each one of them there were available three stages of preparation. Table 1 reproduces the composition of the candy formulation and Table 2 follows the three stages of product development.

Table 1 The composition of the date candy standardized at 1000 g of dry dates.

Ingredients	Amounts
Paste:
Dry dates, pitted (g)	1000
Butter, melted (ml) ^a	66.70
Water (ml)	27.83
Cashew nuts, fine powder (g) ^b	83.30
Pistachios, fine powder (g) ^c	66.70
Coconuts, fine powder (g) ^d	66.70
Almonds, fine powder (g) ^e	66.70
Cinnamon, fine powder (g) ^f	1.25
Cardamon, fine powder (g) ^g	1.25
Rose water (ml) ^h	6.70
Coating:
Coconuts, powder (g)	120

Table 2 The three stages of the development of the date candy.

Stage	Ingredients	wt	wt (%)	Dates : Other Ingredients
1	Rose water	6.70 ml	0.67	96.55 : 3.45
	Water	27.83 ml	2.78
	Date paste	1000 g	96.55
2	Rose water	6.70 ml	0.67	89.88 : 10.12
	Water	27.83 ml	2.78
	Melted butter	66.70 ml	6.67
	Date paste	1000 g	89.88
3	Rose water	6.70 ml	0.48	72.09 : 27.91
	Water	27.83 ml	2.01
	Melted butter	66.70 ml	4.81
	Coconuts	66.70 g	4.81
	Almonds	66.70 g	4.81
	Pistachios	66.70 g	4.81
	Cardamon	1.25 g	0.09
	Cashew nuts	83.3 g	6.01
	Cinnamon	1.25 g	0.09
	Date paste	1000 g	72.09

Chemical Analysis

Stage 3 of the four confections were analyzed for moisture (105° C for 24 hr), ash (450° C for 12 hr), crude protein (Kjeldahl; N × 6.25), gross energy (bomb calorimetry), and crude fat (Soxhlet) according to the AOAC standard methods.[16] Neutral detergent fiber was determined using the method of Van Soest, Roberston, and Lewis.[17] Total carbohydrates were estimated by difference and results are shown in Table 3. Similar work was carried out for a date-based product commercially available in the market.

Besides the proximate/nutritional analysis, preparations were analyzed for minerals (calcium, magnesium, potassium, sodium, and lead in Table 4) and trace minerals (zinc, nickel, manganese, chromium, aluminum, barium, iron, copper, cadmium, arsenic, and selenium). In doing so, the inductively coupled plasma method (ICP) (Perkin Elmer, Optima 33DV, Italy) was employed based on a method described by Al-Hooti, Sidhu, Al‐Otaibi, Al-Ameeri, & Qabazard,[18] and Anonymous.[19] The trace mineral composition can be found in Table 5.

Table 3 Chemical and nutritional composition of Khalas, Umesilla and a commercial date candy standardized at 100 g.

	Khalas candy				Umesilla candy
	Uncooked		Cooked		Uncooked		Cooked		Commercial product
Final product constituents	d.b* ± SD ^a	w.b** ± SD ^a	d.b* ± SD ^a	w.b** ± SD ^a	d.b* ± SD ^a	w.b** ± SD ^a	d.b* ± SD ^a	w.b** ± SD ^a	d.b* ± SD ^a	w.b** ± SD ^a
Gross Energy (kcal)	479.90 ± 0.07	404.43 ± 0.06	476.87 ± 0.05	421.28 ± 0.04	446.09 ± 0.06	376.55 ± 0.05	450.24 ± 0.18	387.71 ± 0.16	438.04 ± 0.05	413.99 ± 0.03
Moisture (g)	15.73 ± 0.31	—	11.69 ± 1.38	—	15.59 ± 0.26	—	13.89 ± .0.13	—	5.49 ± 0.48	—
Ash (g)	1.62 ± 0.03	—	1.75 ± 0.09	—	2.97 ± 0.03	—	3.02 ± 0.07	—	1.97 ± 0.07	—
Fat (g)	1.60 ± 0.67	1.35 ± 0.56	1.53 ± 0.93	1.36 ± 0.82	2.11 ± 0.58	1.78 ± 0.49	1.75 ± 0.15	1.51 ± 0.13	2.91 ± 0.38	2.75 ± 0.35
Protein (g)	5.99 ± 0.12	5.05 ± 0.10	5.34 ± 0.11	4.72 ± 0.90	6.93 ± 0.22	5.85 ± 0.18	6.61 ± 0.13	5.69 ± 0.99	3.32 ± 0.75	3.14 ± 0.71
Fiber (g)	7.10 ± 0.58	5.98 ± 0.50	7.08 ± 0.90	6.26 ± 0.80	6.96 ± 0.85	5.87 ± 0.47	6.58 ± 0.83	5.66 ± 0.43	19.96 ± 0.83	19.59 ± 0.80
Total Carbohydrates (g)	67.96	—	72.61	—	66.60	—	68.19	—	66.35	—

Table 4 The major minerals of Khalas and Umesilla date candies.

Date candy		Ca ± SD ^a	Mg ± SD ^a	K ± SD ^a	Na ± SD ^a	Pb ± SD ^a
Khalas	uncooked	7.63 ± 0.42	10.21 ± 0.80	58.68 ± 0.28	4.68 ± 0.67	0.05 ± 0.20
	cooked	7.72 ± 0.94	10.83 ± 0.81	60.50 ± 2.37	11.87 ± 0.35	0.07 ± 0.05
Umesilla	uncooked	11.40 ± 0.85	10.76 ± 0.72	69.84 ± 1.15	3.514 ± 0.55	0.08 ± 0.02
	cooked	16.41 ± 0.16	11.35 ± 0.87	72.54 ± 1.56	3.612 ± 0.84	0.10 ± 0.07
All units are in ppm.
all samples were done in triplicates.

Table 5 The trace minerals of Khalas and Umesilla date candies.

Date candy		Zn ± SD^a	Ni ± SD^a	Mn ± SD^a	Cr ± SD^a	Al ± SD^a	Ba ± SD^a	Fe ± SD^a	Cu ± SD^a	Cd ± SD^a	As ± SD^a	Se
Khalas	Uncooked	0.26 ± 0.04	0.03 ± 0.01	0.12 ± 0.10	0.03 ± 0.01	0.36 ± 0.09	0.09 ± 0.06	0.44 ± 0.29	0.07 ± 0.02	0.0024 ± 0.001	ND	ND
	Cooked	0.27 ± 0.10	0.04 ± 0.01	0.10 ± 0.03	0.03 ± 0.01	0.49 ± 0.28	0.05 ± 0.01	0.47 ± 0.31	0.05 ± 0.04	0.002 ± 0.001	0.01 ± 0.01	ND
Umesilla	Uncooked	0.19 ± 0.05	0.04 ± 0.01	0.07 ± 0.02	0.03 ± 0.01	0.49 ± 0.14	0.04 ± 0.01	0.24 ± 0.06	0.05 ± 0.01	0.002 ± 0.001	ND	ND
	Cooked	0.22 ± 0.12	0.05 ± 0.01	0.09 ± 0.03	0.03 ± 0.01	0.53 ± 0.19	0.03 ± 0.01	0.21 ± 0.08	0.05 ± 0.02	ND	ND	ND
All units are in ppm.
ND: Not Detected.
All samples were done in triplicates.

Briefly, 1 g triplicates of dried samples were ground and wet digested by addition of 20 mL of concentrated nitric acid. This was let to stand while was covered by a watch glass until the initial reaction subsided. Samples were heated, cooled and 10 mL of 720 g kg⁻¹ perchloric acid was added. The mixture was heated gently then vigorously until clear and colorless. Heating was stopped when the volume of the solution was reduced to about 3 mL. The solution was cooled and transferred to a 100 mL volumetric flask. It was then made to volume, mixed and allowed to stand overnight. The solution was filtered through a filter paper without washing and analyzed by the ICP.

Textural Profile Analysis (TPA)

Each preparation stage of the uncooked and cooked Khalas/Umesilla confection was made into a cylindrical disk (burger-like) of 150 g weight, 14 mm height and 9.4 cm diameter. This was achieved by gently pressing the material in a burger-forming machine. A texture profile analyzer (TA-XT2i from Stable Micro Systems, Surrey, UK) was used to compress the cylinders through the first bite. Data of four textural parameters was obtained (firmness, hardness, brittleness, and adhesiveness/stickiness) using a compression rate of 0.1 mm/s. Samples were compressed to 90% of the original height (12.6 mm) at ambient and refrigeration temperatures (23 and 5° C). The acquisition rate was 5 points per second with the maximum test time not exceeding 100 seconds. Graphs were drawn taking into account the surface area of the cylindrical samples (stress is given in Pa on the ordinate) and the large extent of deformation by deriving the ‘true’ units of strain from the mathematical expression ϵ = ln (L_o /L), where L_o is the original height and L is the height of the sample during compression.[20]

Besides our preparations, a commercial product was also analyzed for texture at ambient temperature using the same operating conditions and parameters described in the preceding paragraph. In a final experiment, date confectioneries were placed in airtight plastic containers and stored at ambient temperature for a period of 13 weeks thus allowing us to record textural variations during aging. Overall, triplicate results of force-deformation spectra upon compression analysis were very similar at each stage of preparation. It was verified that a sample of a particular formulation belonged to the ‘population’ from which it came at a 95% probability limit.

RESULTS AND DISCUSSION

Ingredient Chemistry of the Date Confectionery

To develop a new food product, identification of its composition and nutritional value is a must. This can be related to structural/textural characteristics thus allowing improvement of mouthfeel according to consumer requirements. In this work, the relevant information for our samples was obtained and compared with that of the commercial product. As shown in Table 3, the gross energy content of Khalas and Umesilla candy is higher than for the commercial embodiment. Similarly, the moisture content of our samples is well above that of the commercial product. The latter includes in the formulation a considerable amount of nuts (see fiber in Table 3) that makes the material hard and dry. As we shall discuss in the sensory section of part 2 of this work, dryness affects adversely the mouthfeel of the product.

The fat level of all preparations ranged from 1.53 to 2.91% on a dry basis, which is well within the accepted nutritional requirement for a low fat confectionery formulation.[21] Furthermore, the Khalas and Umesilla candies are fortified in protein, which is almost twice as much as in the commercial product (Table 3). Some protein esterification might have taken place during cooking thus dropping slightly the percentile composition in the cooked variants. Fat and protein are present in small amounts in most of the date cultivars,[5] and the addition of butter and nuts increased their natural levels. As expected, all confections were high in total carbohydrates, a result which is a reflection of the high contents of glucose and fructose in tamar dates.

Proximate analysis of the processed products demonstrated that in terms of moisture, crude fat, crude fiber and crude protein, formulation resulted in higher contents as compared to the dry drupe of Khalas and other varieties.[22] Results of Mustafa, Yousif, and Wahdan[23] on the chemical composition of a plain date paste using the Ruzaiz variety also confirmed that outcome. Clearly, processing results in a shift from a carbohydrate source to an alternative one possessing a diverse range of essential ingredients.

Regarding the minerals, it was mentioned above that burning in a muffle furnace indicated considerable amounts of ash. ICP analysis unveiled a cocktail of microelements and data is presented in Tables 4 and 5. Certainly, the candies are rich in calcium and magnesium which are needed at these levels for bone/teeth growth, pregnancy, lactation, the heart and lungs. Sodium is low, but potassium is high being vital for the maintenance of the body fluids and electrolyte balance. There are small amounts of lead also reported for dry dates by Al-Hooti, Sidhu, and Qabazard.[24] The formulations also include 9 confirmed trace elements which are necessary for good health.[6] Selenium and arsenic were not identified probably because they fell below the detection sensitivity of the technique (0.002 ppm). Variations observed in microelements between the cultivars of Khalas and Umesilla can be influenced by soil fertility and the amounts of fertilizer used.[25]

Textural Properties of the Date Confectionery

The traditional technique of compression testing was used to monitor the textural properties of candies through the first ‘bite’ (cycle). These were made with dates being apart an order of magnitude in their retailing price (Khalas costs about 2.6 U.S.$ per kilo). One of the objectives of this work was to reproduce the textural properties of a good quality candy using as raw material the affordable Umesilla variant. The parameters of firmness, hardness, brittleness and adhesiveness were identified as indicative of textural quality, and the remaining of the manuscript will present a concise account of their development as a function of the three stages of preparation and cooking temperature.

Fig. 1 illustrates a typical example of a force-deformation profile obtained following extensive compression at 5° C of the uncooked Khalas candy. Stage 1 shows a relatively weak structure without a maximum force occurring at any time during the first cycle compression (hardness). Addition of butter at stage 2 of the formulation reinforces the rigidity of the material at refrigeration temperature. The textural profile is reminiscent of a spreadable paste exhibiting considerable plasticity.[26] Extensive transformation of the textural behavior is monitored upon addition of ground nuts to the paste at the final stage of preparation. A breakdown profile typical of a strong food system yields a hardness value of 35 kPa. The topology of the material is envisaged as a soft date paste reinforced by the hard nut particles being dispersed evenly in the continuous matrix.

Figure 1 Stress-strain profile of the cooked Khalas date candy at stages 1, 2 and 3 of formulation following compression at 5° C (compression rate = 0.1 mm/s).

The deformation required to achieve the first significant drop in the stress-strain curve pinpoints the brittleness (anti-elasticity) of the final product, which is found to be about 0.3 units of strain in Fig. 1. This value falls easily within the family of brittle foodstuffs (27), and it should be attributed to the broad interfacial area between the continuous matrix and the filler particles that increases the localized stress effects. All along, the initial slope of the force-deformation curve (from 0 to 0.03 units of strain) was considered to be the firmness (modulus) of the material, and it exhibited a five-fold increase as the product evolved from stage 1 to 3. Similar results were recorded for the uncooked Umesilla preparation. The cooked versions of both candies were qualitatively congruent with this description but displaced to higher values of hardness due to some water loss incurred while cooking.

The influence of temperature of compression is discussed in Fig. 2, which depicts data at 23° C. This is a particular relevant temperature since it reflects the storage conditions of the product in the market. The first stage of preparation of the cooked Khalas candy is similar to the corresponding sample compressed at 5° C in Fig. 1. Therefore, the consistency of the date paste is not affected significantly within this temperature range. Addition of butter reinforced the structure of the material at refrigeration temperature but the ingredient remains largely liquid-like at 23° C thus weakening the matrix of stage 2. The stress-strain curve is reminiscent of a thick viscous foodstuff rather than a plastic dispersion.[28] The final product remains relatively soft, as compared with its textural profile at 5° C, following the addition of powdered nuts. Furthermore, the characteristic peak of rupturing the gel-like material at low temperatures is now lost. As before, the large deformation properties of the Umesilla candy with or without the thermal treatment broadly coincided with those in Fig. 2.

Figure 2 Stress-strain profile of the cooked Khalas date candy at stages 1, 2, and 3 of formulation following compression at 23° C (compression rate = 0.1 mm/s).

The soft, paste-like consistency of our candies contrasts dramatically with the results obtained for the commercial product. Fig. 3 reproduces the stress-strain curve at 23° C of two embodiments made with powdered pistachios or coconut. Sharp breakdown profiles typical of very strong food materials are recorded due to the low moisture content and the inclusion of high levels of nuts in the formulation (Table 3). Thus hardness developed from below 40 kPa at 5° C (Fig. 1), to 95 kPa (coconut) and 140 kPa (pistachios) at 23° C for the samples in Fig. 3. The excessive yield stress of the commercial material reflects upon its adhesiveness, which is virtually zero. On the other hand, our formulations exhibited considerable adhesiveness at ambient temperature (e.g., 140.2 N mm).

Figure 3 Stress-strain profile of a commercial date candy compressed at ambient temperature (23° C) and containing pistachios (1) or coconuts (2) (compression rate = 0.1 mm/s).

Finally, we studied the textural stability of the date candy over a period of three months, which is the maximum time reported by retailers for purchase of the product. Fig. 4 illustrates the brittleness values during aging but similar conclusions are drawn for the remaining textural parameters. Clearly, the overall structural relaxation was maintained at ambient temperature. Furthermore, no significant difference was noticed between the two candies in terms of these quality criteria.

Figure 4 Effect of aging at ambient temperature on the brittleness of the (□) uncooked Khalas, (⋄) cooked Khalas, (▵) uncooked Umesilla, and (○) cooked Umesilla date candies.

CONCLUSIONS

Correlation of chemical characteristics and composition of the fabricated products with textural results was shown to be extremely encouraging. Recently, a similar level of success was achieved in the building up of a relationship between TPA attributes and moisture content of dried dates, which unveiled the “plastic” or “elastic” nature of the date flesh.[29] These promising developments encouraged us to fully develop an inexpensive candy using a processing date in part 2 of this series. The plasticity and adhesiveness of the paste to the palate were fully investigated via a trained sensory panel that allowed handshaking of the consumer's perception to instrumental textural attributes.

ACKNOWLEDGMENT

Support from the project: “Improvement of date palm production and dates quality in the Sultanate of Oman” (SR/AGR/PLNT/01/01) is acknowledged. M. AL-Yahyaie, A. Ritchie and K. Annamalai are thanked for technical support.

Notes

^aAsli Pure Butter

^bShahi Cashew nuts

^cShahi Pistachios

^dShahi Coconuts

^eShahi Almonds

^fShahi Cinnamon

^gShahi Cardamom

^hAl-Rabee rose water(Lebanon).

*Dry based,

**wet based,

^astandard deviation.

^astandard deviation.