EFFECT OF APPLE POMACE INCORPORATION ON RHEOLOGICAL CHARACTERISTICS OF WHEAT FLOUR

Abstract

Different levels of apple pomace with different particle size at each level were blended with wheat flour as a source of dietary fiber and the blends were evaluated for their rheological characteristics. Farinographic water absorption increased from 59.1 ml in control to 69.4, 68.2 and 70.2 ml in blends with 11 percent pomace of 30, 50 and 60 mesh, respectively. Wheat flour took 1.9 min. for dough development and the corresponding values for blends containing 11 percent of 30, 50 and 60 mesh pomace were 3.9, 3.8 and 3.8 min., respectively. Mixing tolerance of the blends with 11 percent of 30, 50 and 60 mesh pomace increased to 85.0, 92.5. and 97.5 BU as against 67.5 BU in case of control (wheat flour). Dough stability increased slightly upto 8 percent pomace level but decreased at higher levels of pomace. Gelatinization temperature did not show any remarkable change with pomace incorporation upto 11 percent. Peak viscosity decreased when pomace level was increased from 0 (control) to 5 percent but thereafter it increased. Temperature at peak viscosity did not show much variation between the blends.

INTRODUCTION

Inadequate fiber intake has been found to be associated with diseases like diverticulosis (Painter and Burkitt, 1997), atherosclerosis (Trowell, 1972), colonic cancer (Burkitt, 1971) and appendicitis (Walker et al., 1973). During the past century, the dietary fiber intake has decreased considerably (Cumings, 1973). The fiber content of flour has also been reduced since the beginning of current century due to a change in milling process where by flour is now highly refined. Different plant fibers are added to various baked food products in order to increase their fiber content. Cereal brans and hulls of legumes are some of the common sources which are used for fiber supplementation of foods. Despite brans and hulls being very rich source of total dietary fiber, technologists and nutritionists have restricted themselves in making use of such materials in food products because of their phytate content and lack of soluble dietary fiber. Apple pomace, a solid material that remains after extraction of juice from fruit, is not only a good source of total dietary fiber but contains a significant amount of soluble dietary fiber which comprises pectin and is devoid of phytate. Some attempts have been made to incorporate apple pomace in some baked products (Wang and Thomas, 1989; Carson et al., 1994) but information regarding the effect of apple pomace on rheological characteristics of wheat flour is scarce. The present study was thus undertaken to know the effect of apple pomace incorporation on farinographic and amylographic characteristics of wheat flour.

MATERIALS AND METHODS

Apple Pomace

Apple pomace was obtained from apple juice concentrate plant of Jammu and Kashmir Horticultural Produce Processing and Marketing Corporation (JKHPMC) located at Doabgah Sopore, Jammu and Kashmir. It was dried in a cabinet drier at a temperature of 58 ± 2°C. Seeds, stems and other extraneous material was removed from pomace manually. It was then ground in a hammer mill (Fitz) and passed through sieves of 30, 50 and 60 mesh in order to get pomace of different particle size.

Preparation of Blends

Wheat flour and pomace were blended in following proportions.

Wheat Flour (kg)	Pomace (kg)
98	2
95	5
92	8
89	11

The blends were mixed thoroughly and then sieved thrice to achieve uniform mixing. The blends were stored in HDPE containers at ambient temperature for further use.

Farinographic Characteristics

Farinographic tests for wheat flour and various blends were conducted using a Brabender Farinograph equipped with a 50 g stainless steel bowl. The constant flour weight procedure was used for getting the farinograms (Method 54-21 AA CC, 1983). Volume of water required to produce a curve with a maximum resistance centered on 500 BU line was recorded. Farinograms were interpreted in terms of dough development time, dough stability and mixing tolerance index.

Amylographic Characteristics

Gelatinization and pasting characteristics of wheat flour were measured with the help of viscoamylograph (C.W. Brabender, Duisburg, Germany) by the method of Halick and Kelly (1959). Sample weighing 65 g was mixed with 450 ml water and the slurry thus formed was transferred to the amylograph bowl. Amylograms were obtained by heating the sample from 30 to 95°C and were interpreted in terms of gelatinization temperature, peak viscosity and viscosity at 95°C.

RESULTS AND DISCUSSION

Farinographic Characteristics

The results of farinographic characteristics of various flour-pomace blends are given in Table 1 and the farinograms are shown in Figure 1. It is evident from the data that as the percentage of pomace in blend increased, there was a significant (P < 0.05) increase in farinographic water absorption. The farinographic water absorption of blends containing 30 mesh pomace increased from 59.1 to 69.4 ml when the pomace level was increased from 0 (control) to 11 percent. The corresponding values for the blends with 50 and 60 mesh pomace increased to 68.2 and 70.2 percent respectively. An increase in water absorption of blends was observed with decrease in the particle size of pomace in it. This can be attributed to increase in surface area of pomace which holds more water. The results of the present study are in agreement with those of Pomeranz et al. (1976), Lorenz (1976) and Krishnan et al. (1987). Arrival time of blends containing upto 5 percent pomace of any particle size was less than that of control. However, at higher levels, it was more than that of control. At 0 percent (control) pomace level, the arrival time was 1.5 min. and it increased to 2.3, 2.1 and 2.1 min. in blends containing 11 percent 30, 50 and 60 mesh pomace, respectively. It was also observed that arrival time decreased with decrease in particle size. However, difference in arrival was not prominent between blends containing 50 and 60 mesh pomace. Dough development time increased with the increase in pomace level and the increase was more prominent in blends containing pomace of larger particle size. Wheat flour took 1.9 min. for dough development and the corresponding values for blends containing 11 percent of 30, 50 and 60 mesh pomace were 3.9, 3.8 and 3.8 min. respectively. Earlier workers have also reported similar results while using wheat bran as a source of dietary fiber (D'Appolonia and Youngs, 1978; Rao and Rao, 1990).

Table 1. Effect of Level and Particle Size of Pomace on Farinographic Characteristics of Wheat Flour-Pomace Blend

Particle Size (Mesh No.)	Pomace Level (%)	Water Absorption (ml)	Arrival Time (min)	Dough Dev. Time (min)	Mixing Tolerance Index (BU)	Dough Stability (min)	Softness (BU)
Control	0	59.1	1.5	1.9	67.5	3.7	80.0
30	2	61.5	1.3	2.1	62.5	3.8	77.5
	5	65.7	1.4	3.0	77.5	3.8	112.5
	8	67.2	1.7	3.8	88.0	3.8	115.0
	11	69.4	2.3	3.9	85.0	2.8	135.0
50	2	61.5	1.2	2.1	75.0	3.1	95.0
	5	63.8	1.4	2.5	70.0	4.2	110.0
	8	66.9	1.5	3.3	92.0	3.9	125.0
	11	68.2	2.1	3.8	92.5	2.8	130.0
60	2	63.4	1.3	2.1	77.5	3.3	87.5
	5	64.0	1.2	2.3	70.0	4.1	100.0
	8	67.9	1.5	3.5	92.5	3.6	132.5
	11	70.2	2.1	3.8	97.5	3.0	137.5
CD (Particle size)		0.16	0.06	0.07	5.93	0.17	3.67
CD (Level)		0.20	0.07	0.09	7.66	0.22	4.73
CD (Interaction)		0.36	0.13	0.17	13.28	0.38	8.20

All values are the average of two observations.

Figure 1. Farinograms of flour-pomace blends.

Mixing tolerance, in general, increased with the increase in level of pomace, indicating higher resistance to weakening of dough during mixing. It increased from 67.5 BU in control to 85.0, 92.5 and 97.5 BU at 11 percent level of 30, 50 and 60 mesh pomace, respectively. Sharma (1994) made similar observations while working on incorporation of stabilized rice bran in bread. Dough stability increased with the increase in pomace level upto 8 percent and thereafter it decreased. Wheat flour had a dough stability of 3.7 min. which increased slightly upto 8 percent of 30 and 50 mesh pomace level but decreased significantly at pomace levels greater than 8 percent. Similarly in the blends with 60 mesh pomace, dough stability increased significantly upto 5 percent pomace level and decreased thereafter. At 11 percent pomace level, the stability of all the blends was lower than control. Effect of particle size of pomace was non-significant on dough stability. Sharma (1994) reported a continuous increase in dough stability with increase in bran level which is contrary to the results of this study. The difference can be attributed to the variation in chemical nature of the two fiber sources. Dough softening increased significantly with an increase in pomace level but particle size had an insignificant effect on dough softening.

Amylographic Characteristics

Amylographic characteristics of wheat flour as affected by different levels and particle size of pomace are shown in Table 2 and the amylograms are show in Figure 2. No remarkable difference in gelatinization temperature of wheat flour and blends containing pomace was observed. Results of peak viscosity showed a specific trend in the blends with different levels of pomace. It initially decreased when pomace level was increased from 0 (control) to 5 percent but thereafter it increased. The control samples had a peak viscosity of 570 BU. At 5 percent pomace level, the peak viscosity values were 510, 495 and 480 BU for blends with 30, 50 and 60 mesh pomace, respectively. The corresponding values at 11 percent pomace level were 640, 645 and 695 BU. The initial decrease in peak viscosity with increase in pomace level upto 5 percent may be attributed to dilution of starch and gluten of wheat flour. The increase in peak viscosity with further increase (above 5%) in pomace level may be attributed to gelling effect of pectin present in pomace and water binding by pomace. At 8 and 11 percent pomace level, the pectin is present in sufficient quantity to form a gel and to cause an increase in the viscosity. Peak visosity temperature did not vary with the change in pomace particle size or its level. It ranged between 86.7 and 87°C for control and blends with different levels of pomace. Results of viscosity at 95°C showed almost similar trend as that of peak viscosity. It was 405 BU for control and decreased to 380, 350 and 350 BU as the pomace level was increased to 5 percent in blends with 30, 50 and 60 mesh pomace, respectively. At 11 percent pomace level, the corresponding values increased to 500, 495 and 540 BU for blends containing 30, 50 and 60 mesh pomace, respectively. Higher values of viscosity at 95°C in case of blends with 60 mesh pomace is attributed to the fineness of pomace as a result of which more pectin comes into slurry and participates in gel formation. Further more, fineness results in more binding of water.

Table 2. Effect of Particle Size and Level of Pomace on Amylographic Characteristics of Wheat Flour-Pomace blends

Particle Size (Mesh No.)	Pomace Level (%)	Gelatinization Temperature (°C)	Peak Viscosity (BU)	Peak Viscosity Temp. (°C)	Viscosity at 95°C (BU)
Control		7.5	570	87.5	405
30	2	59.0	505	87.5	380
	5	59.7	510	87.5	380
	8	59.7	585	86.7	440
	11	59.7	640	87.5	500
50	2	59.7	495	86.7	350
	5	59.7	495	86.7	350
	8	58.2	575	86.7	420
	11	59.7	645	87.8	495
60	2	59.0	530	86.7	380
	5	59.0	480	86.7	350
	8	59.0	600	87.5	440
	11	59.7	695	87.5	540

Figure 2. Amylograms of flour-pomace blends.

CONCLUSION

It is concluded that incorporation of apple pomace in wheat flour results in higher energy requirements for dough mixing and slightly more time is required for dough development when pomace is incorporated in wheat flour.

Acknowledgments