EFFECT OF TOMATO SEED MEAL SUPPLEMENTATION ON THE DOUGH AND BREAD CHARACTERISTICS OF WHEAT (PBW 343) FLOUR

ABSTRACT

Deoiled seed meal from tomato processing waste was used to supplement wheat flour (PBW 343) at 10, 20 and 30% levels to study the effect on rheological and baking properties. Farinograph indicated increase in water absorption, dough development time, dough stability, departure time and valorimeter values, while, decrease in the mixing tolerance index and degree of softening with the increase in meal levels. Viscoamylogram showed decrease in pasting peak, peak viscosity, viscosity at 95°C, visco sity at 50°C and set back on cooling whereas the falling number values also declined. Baking properties indicated increase in loaf mass, decrease in loaf/specific loaf volume and sensory score with the increased levels of meal. The bread supplemented with 10% deoiled seed meal exhibited good sensory characteristics and improved protein quality.

INTRODUCTION

Food processing industry produces huge quantities of bio-degradable wastes that cause environmental pollution during the course of decomposition. These wastes contain good quality nutrients that could be utilised as food, feed or fertiliser. The tomato processing generates about 7.0–7.5% solid waste of raw material and pomace constitutes about 71–72% of this waste.1-2 Seeds, the major part of the pomace, contain 22.2–33.9% proteins and 20.5–29.6% lipids.[1], 3-6 The seed protein could be extracted to produce protein concentrate/isolate.[2], 6-10 Functional properties of tomato seed proteins have been evaluated and found to be comparable with other plant proteins.[2], 10-12 The nutritional quality of tomato seed proteins has been found equivalent to commonly used plant proteins as evident from amino acids score, growth of micro-organism (Tetrahymena pyriformis), proteolytic activity and rat feeding trials.[2], [11], [13] The seed protein is rich in lysine i.e., 80–100 g/Kg N14-15 and can supplement products that are deficient in this amino acid like cereals.[5], 16-17 No anti-nutritional factor or harmful constituent have been reported in tomato seeds[11] that make it better source of protein over other non-conventional sources.

Commercial untreated seed meals at 5, 10, 15 and 20% levels have been incorporated into wheat flour.[5] The whole meal at 20% level does not show any significant change in staling rate while the loaf volume increases by 20.4%, however, 20% level of defatted seed decreases the specific loaf volume by 72%. The whole and defatted meals at 5, 10 and 15% levels in balady bread improved water absorption, dough development time and dough stability.[17] The defatted meal comparatively decreased mixing tolerance index and dough weakening. The dough extensibility, resistance to extension and dough energy were minimised while the gas production, moisture content and loaf diameter after baking were improved with the increase in tomato seed meal contents. Organoleptic evaluation showed that balady bread with 10% seed meal received a fancy grade.

Present study was designed to evaluate the effect of seed meal isolated from waste on rheological and baking properties of wheat flour in order to improve the protein quality of bread.

MATERIALS

Tomato seeds were separated from the pomace, collected from a tomato paste manufacturing plant located at Amritsar (India), by sedimentation technique[18] and dehydrated at 70°C for 5 h in a cabinet dryer.[2] Seeds were ground using hammer mill (M/S Narang Scientific works, New Delhi), extracted with hexane, desolventised and ground again to pass through 85 mesh sieve to obtain fine powder termed as deoiled seed meal.

Certified variety of wheat, PBW 343, was procured from Punjab Agricultural University, Ludhiana, India. It was conditioned to 14% moisture and milled using laboratory mill (Brabender OHG Duisburg, Germany) to obtain flour with 70% extraction rate. Milled samples were stored in airtight containers for further use.

METHODS

Wheat Flour Quality

The quality was evaluated using gluten, sodiumdodecylsulphate(SDS)-sedimentation value, damaged starch and diastatic activity following standard methods of A.A.C.C.[19] Moisture and ash contents were determined using standard analytical techniques of A.O.A.C.[20]

Dough Characteristics

Rheological properties of the wheat flour supplemented with deoiled meal were studied at 0, 10, 20 and 30% replacement levels using Farinograph (Brabender, Germany), Viscoamylograph (Brabender, Germany) and Falling number apparatus (Perten, Sweden) following standard methods of A.A.C.C.[19]

Bread Characteristics

Straight dough formulation was used in bread making. All ingredients i.e., wheat flour (200–140 g), water (variable), compressed yeast (6 g), salt (2 g), sugar (10 g) and additive (deoiled tomato seed meal, 0–60 g) were mixed for 1.5 min and allowed to ferment at 30°C and 85% RH in the fermentation cabinet for 90 min. The loaves were mechanically moulded, proofed for 25 min at the same temperature as well as humidity followed by baking at 220°C for 25 min in a rotary oven (M/S National manufacturing Co., England). The un-sliced loaves were cooled to room temperature, placed in coded polyethylene bags and stored at 27°C and 65% RH till use.

Loaf volume was measured 1 h after baking using rapeseed displacement method.[21] Sensory evaluation of bread for crust and crumb characteristics such as texture and eating quality was carried out after 24 h of baking by a panel of six semi-trained judges. Texture was evaluated in terms of softness and hardness on a 6-point scale with scores of 1 and 6 for hard and soft respectively. Eating quality was evaluated in terms of acceptability on a 4 point scale with scores 1 and 4 for very poor and excellent respectively.

Firmness was measured on universal testing machine (Instron Corporation, USA) using 25 mm thick slices selected after discarding the outer slices (∼60 mm from each end). Rate of compression or crosshead speed was set at 100 mm/min. A load cell (100 Newton) and flat aluminium plunger with diameter of 36 mm (area 1017.9 mm²), were used to compress the above slices up to 40%.[19] The test was repeated on three different slices. Firmness (Compression value) and softness indices (Ratio of compression value at time ‘t’ to that of at 2 h) of bread were measured 2, 24, 48, 72 and 96 h after baking.

Statistical Analysis

Data were statistically analysed using ANOVA to test the significance of differences amongst test and control values according to Gomez and Gomez.[22] Least significant difference (LSD) was also calculated in case of significant effects of supplementation levels and storage.

RESULTS AND DISCUSSION

Deoiled tomato seed meal contained protein, lipid, ash, crude fibre and moisture content of 33.07, 1.05, 30.24 and 7.77% (dry basis) respectively. The incorporation of deoiled meal containing high protein, into wheat flour would improve the protein quality of bread. More over, tomato seed protein is rich in lysine, whereas, wheat flour protein is deficient in this essential amino acid. Therefore addition of tomato seed meal to wheat flour may improve the overall protein quality.

Wheat Flour Quality

Suitability of the wheat flour quality for bead making was evaluated. The analytical data (14% moisture basis) showed that the ash, damaged starch, wet and dry gluten contents of wheat flour (PBW 343) were 0.67, 4.34, 25.35, 9.45% while the SDS-sedimentation value and diastatic activity were 32 mL and 240 mg/10 g flour respectively. The ash content of flour decreased with the decrease in extraction rate. Yaseen et al.[17] reported ash content of 1.86% for 82% extraction rate and thus provide support to the present results where the extraction rate was 70%. The damaged starch content of the flour was normal indicating good milling conditions. Wet and dry gluten contents of flour indicated that the wheat variety (PBW 343) was suitable for bread making. SDS-sedimentation values indicated that the wheat was medium hard and also confirmed its suitability for bread making. The diastatic activity value indicated that wheat was sound without any rain damage or sprouting. Recently, Sidhu[23] reported the wet gluten (25.50%), dry gluten (9.00%), ash content (0.62%), damaged starch (4.2%), SDS-sedimentation value (29 mL) and diastatic activity (534.0 mg/10 g flour) for the same wheat variety (PBW 343), which supports the present results.

Dough Characteristics

The dough characteristics (Table 1) of wheat flour and deoiled meal blends indicated that the water absorption, dough development time, dough stability, departure time and valorimeter values increased, while, the mixing tolerance index and degree of softening decreased with the increase in level of seed meal incorporation up to 30%. Earlier reports[17] on incorporation of deoiled meal up to 15% indicated an increased water absorption, constant dough development time and decreased dough stability and mixing tolerance index, which corresponds to the present findings.

Table 1. Effect of Tomato Seed Meal Supplementation on Rheological Properties of Wheat (PBW 343) Flour

	Tomato Seed Meal
Parameters	0%	10%	20%	30%
Dough characteristics
Water absorption, %	59	61	62.8	63.2
Dough development time, min	2.0	2.5	2.5	3.5
Dough stability, min	6.6	7.5	8.0	8.5
Departure time, min	7.5	8.5	9.0	9.5
Mixing tolerance index after 5 min, BU*	60	50	30	10
Degree of softening after 10 min, BU	110	90	70	40
Valorimeter value	44	45	48	50
Pasting properties
Gelatinisation temperature, °C	60	60	60.5	60.5
Pasting peak, °C	90	89.5	89	88.5
Peak viscosity, BU	340	310	250	230
Viscosity at 95°C, BU	250	220	160	150
Viscosity at 95°C after 15 min cooking, BU	240	210	150	140
Viscosity at 50°C, BU	480	430	310	250
Set back on cooling, BU	240	220	160	110
Falling number, sec	616	582	462	313

*Brabender Unit.

The gelatinisation temperature remained constant while pasting peak, peak viscosity, viscosity at 95°C, viscosity at 50°C and set back on cooling decreased with the increase in levels of deoiled meal. The effect of deoiled meal addition on pasting properties of dough could not be traced in literature. However, It might be due to dilution effect of deoiled meal as well as increase in protein content per unit weight of the sample.

The falling number values declined with the increased incorporation of deoiled meal into the wheat flour, indicating high α-amylase activity. Since the deoiled meal was obtained from seeds of tomatoes processed through hot break process, the observed decline in falling number value might be due to the dilution effect on the starch content of the dough resulting in lower viscosity and the falling number values.

Bread Characteristics

The loaf weight (Table 2) increased significantly (P<0.05) with the addition of deoiled meal at 10% level however further increase in the level of meal incorporation did not have significant effect. The increase in loaf weight can be attributed to the higher water absorption capacity of the deoiled meal. Yaseen et al.[17] observed a similar increase in the weight of balady bread. Loaf volume for control was maximum and decreased significantly with incorporation of deoiled meal. These results are in accordance with those of Knorr and Betschart[24] who reported a depression in loaf volume for protein-enriched breads. Specific loaf volume followed similar trends as loaf volume, which can be attributed to the reduction in gluten content of flour as a result of deoiled meal incorporation. Earlier report also indicated a decrease of 72% in specific loaf volume of bread with the addition of 20% deoiled tomato seed meal.[5] However, Yaseen et al.[17] reported an increase in the diameter of balady bread with increase in level of deoiled meal as compared to control.

Table 2. Effect of Tomato Seed Meal Supplementation on Loaf and Crumb Characteristics of Wheat (PBW 343) Bread

	Loaf (n=3)			Crumb (n=6)
Meal, %	Weight, g	Volume, mL	Specific Volume, mL/g	Texture Score	Eating QualityScore
0	292±2^a	700±5^a	2.40±0.2^a	5.8±0.41^a	3.3±0.5^a
10	300±6^b	651±5.57^b	2.17±0.1^b	4.0±0.9^b	2.7±0.5^b
20	301±2^b	560±6^c	1.86±0.01^c	2.8±0.6^c	1.8±0.6^c
30	305±3^b	562±4^c	1.84±0.0^c	2.7±0.5^c	1.5±0.5^c
LSD	6.4	8.4	0.06	1.1	0.6

Mean±S.D. values superscripted with dissimilar letters in columns are significantly different (p<0.05).

The crumb texture and eating quality scores indicated a significant decrease in sensory characteristics with the incorporation of deoiled meal. The texture score was low because of hardness as a result of lower loaf volume. Eating quality score also decreased as a result of change in flavour and colour scores. The flavour was affected due to a characteristic taste and odour contributed by the deoiled meal. However bitterness was not observed as reported by Sato and Sakamura.[25] The colour became darker due to maillard reaction accelerated by higher lysine content of deoiled meal protein.[14] Yaseen et al.[17] reported composite scores of 87.1, 88.7, 82.3 and 62.3% for crumb and crust characteristics of Balady bread with 0, 5, 10 and 15% incorporation levels of deoiled meal respectively. Carlson et al.[5] reported that 23 out of 30 penalists selected the bread containing 20% whole tomato seed meal based on odour score. Thus present findings are in agreement to the earlier reports.

The firmness values (Table 3) revealed a significant increase with increase in the levels of deoiled meal as well as storage. Softness index followed a similar pattern as for firmness and after 96 h their values became almost double at all the levels of meal supplementation. It was observed that staling rate for control was slightly higher than that for deoiled meal containing breads, however, Carlson et al.[5] did not find any significant change in staling rate up to with 20% level of whole meal incorporation. However, present study revealed that the bread with 10% level of incorporation was acceptable considering the physical and sensory characteristics.

Table 3. Effect of Tomato Seed Meal on Firmness and Softness Index Values of NM Crumb Slices from Wheat (PBW 343) Bread, (n=3)

		Storage Period, h
Parameter	Deoiled Meal, %	2	24	48	72	96	LSD
		0	3,260^ap	5,816^bp	6,850^bp	7,386^bp	7,751^bp
Firmness, N/m^2	10	7,017^aq	8,503^ap	13,110^bq	17,700^cq	18,650^cq	2,528
	20	10,300^ar	16,140^bq	19,500^cr	20,000^cq	20,450^cq
	30	10,730^ar	17,190^bq	19,800^cr	20,400^dq	20,790^dq
	LSD				2,826
Softness index	0	1.00^ap	1.78^bp	2.10^bp	2.27^bp	2.38^bp
	10	2.15^aq	2.61^ap	4.02^bq	5.43^cq	5.72^cq	1.00
	20	3.16^ar	4.95^bq	5.98^cr	6.13^cq	6.27^cq
	30	3.29^ar	5.27^bq	6.07^cr	6.26^cq	6.38^cq
LSD				0.50

Means superscripted with dissimilar letters in rows and columns are significantly different (p<0.05).

CONCLUSIONS

The wheat cultivar PBW 343 is suitable for bread making. Addition of deoiled seed meal improved the total protein content and overall protein quality, however, rheological and baking properties were affected. The 10% level of meal could be successfully employed to improve the nutritional value along with other quality characteristics.

ACKNOWLEDGMENT

The authors are thankful to University Grants Commission, New Delhi for granting a Major Research Project.