[Advances in Food Research] Advances in Food Research Volume 8 Volume 8 || The Blanching Process

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<ul><li><p>THE BLANCHING PROCESS </p><p>BY FRANK A. LEE </p><p>New Y'ork State Agricultural Experiment Station, Cornell Uniuersity, Geneua, New York </p><p>I. Introduction . . . . . . . . . . . . . . 1. Mineral Substances . . . . . . . . . . . 2. Sugars and Proteins . . . . . . . . . . . 3. Carotene . . . . . . . . . . . . . 4. Thiamine . . . . . . . . . . . . . 5. Riboflavin . . . . . . . . . . . . . 6. Niacin . . . . . . . . . . . . . . 7. Ascorbic Acid (Vitamin C ) . . . . . . . . . 8. Chlorophyll . . . . . . . . . . . . . 9. Sulfur Compounds . . . . . . . . . . . </p><p>10. Enzymes . . . . . . . . . . . . . 111. Special Techniques for Blanching . . . . . . . . . </p><p>1. Steam Pressure . . . . . . . . . . . . 2. Electronic Blanching . . . . . . . . . . . </p><p>a. Weight Changes . . . . . . . . . . . 3. Special Treatments . . . . . . . . . . . </p><p>Unblanched Material . . . . . . . . . . . V. Summary . . . . . . . . . . . . . . </p><p>References . . . . . q . . . . . . . </p><p>11. Changes in Nutrients and Other Substances During Blanching . </p><p>IV. Recent Studies on Fundamental Changes During Frozen Storage of </p><p>Page 63 65 65 68 72 74 75 75 76 81 83 84 88 86 87 87 91 </p><p>95 104 106 </p><p>I. INTRODUCTION </p><p>The preservation of vegetables for relatively long term storage is a very important industry. Indeed, the canning of peas in the United States alone amounted to 31,222,000 cases for the year 1955. As far as the frozen product is concerned, 231.2 million pounds were packed in that year (Western Canner and Packer, 1956). </p><p>One of the important processes in the preparation of vegetables for freezing, canning, or dehydration, is blanching, or as it is sometimes called, scalding. </p><p>The process of blanching involves the treatment by means of some form of heat, usually either steam or boiling water. The time and tem- perature used depend upon the final processing to be employed, as well </p><p>63 </p></li><li><p>64 FRANK A. LEE </p><p>as on the nature of the material to be packed. Other means to achieve this end have been studied. </p><p>Blanching as a pretreatment of vegetables for canning has as its object (1 ) the removal of tissue gases; (2) the shrinking of the material so that adequate fills can be had in the can; and ( 3 ) the heating of the material prior to filling so that a vacuum will be obtained after heat processing and boiling. The first of these is necessary to reduce internal stresses in the can, which in turn, tend to avoid such undesirable results as buckling. The second of these makes it possible to meet the legal requirements concerning fill. While it is true that the process used for the removal of the tissue gases will at the same time inactivate any enzymes present, it might well be noted that if some were left intact, the cooking process, so necessary in canning to effect sterilization, would complete the inactivation of the enzymes. It is for this reason that enzyme inactivation, per se, in blanching as a part of the canning process is not so important, </p><p>Blanching is necessary as a part of the preparation for freezing preservation ( I ) to inactivate the enzymes in the tissues and ( 2 ) to shrink the material so as to conserve space in packing. The inactivation of the enzymes is very important in this process because no final cook or sterilization is used previous to freezing, and freezing storage, at least at the temperatures commonly employed, does not prevent unde- sirable deterioration in flavor, odor, and color on the part of the enzymes in the tissues. Enzyme inactivation in material to be dehydrated is important, because again, no further cooking previous to storage, is involved. </p><p>In the early days of the preservation of vegetables by freezing, it was found that mere storage at -18OC. ( O O F . ) did not prevent the develop- ment of off-flavor, off-odor, and off-color in the stored products. The early work of Joslyn and Cruess (1929) in this connection is summarized as follows. </p><p>These workers showed that steam or water blanch at 100OC. (212OF.j for 2 5 minutes, followed by chilling in cold water or a blast of cold air and packing in brine in the case of certain vegetables resulted in vegetables which were considered to be equal to the fresh even after several months of storage at -18 to -9.5OC. (0-15OF.). </p><p>In 1930, Barker recorded work on the preservation of vegetables by freezing in which samples of peas were stored at each of the folIowing temperatures: -so, -50, -100, and -18C. (27OF., 23OF., 14OF., and O O F . ) for four weeks, and then thawed and cooked. At each tem- perature autolytic changes occurred affecting the color and flavor. The autolysis was markedly retarded at the lower temperatures but even at </p></li><li><p>THE BLANCHING PROCESS 65 </p><p>-18OC. (OOF.) slight changes occurred, and an objectionable flavor appeared although the color was normal, </p><p>A means of preventing these autolytic changes was found in blanch- ing, i.e., partial cooking, before freezing. Peas cooked for about 8 minutes, and then frozen in water a t -18OC. (0F.) were stored suc- cessfully for 4 months, and there seemed no reason why this period could not be extended. After thawing and further cooking, the color was still excellent, and there was no trace of the distasteful flavor noted in peas frozen without preliminary blanching. The success of the blanching was presumed to be due to the destruction of the catalytic systems by the heat. </p><p>While blanching times and perhaps methods of storing have changed somewhat, it is quite obvious that these workers twenty-eight years ago expressed views that were fundamentally sound. The necessity of the blanching step in the preparation of vegetables for freezing, for canning, and for dehydration has been demonstrated on many occasions since then. This step is now universally employed under commercial condi- tions, and it is recommended to home processors by the books and bulletins on this subject. </p><p>Adam et al. (1942) concluded that blanching has an appreciable effect on the pressures developed in the cans and on the total weight of contents. They considered it necessary, but stated the times should be as short as practicable. </p><p>II. CHANGES I N NUTRIENTS AND OTHER SUBSTANCES DURING BLANCHING </p><p>Many studies were conducted to determine the effects of steam and water blanching on the vegetables so processed. Much of this work was done to determine whether steam or water blanching is the more efficient when one considers the loss of nutrients as a result of blanching. In certain of these studies, time and temperature of the blanch were an important part of the work. </p><p>1. MINERAL SUBSTANCES Horner ( 1936-1937a ) observed that during blanching, considerable </p><p>loss of potassium and phosphates occurred in all vegetables. Shrinkage of the vegetables, accompanied by a reduction in weight took place also. </p><p>In the following blanch times, peas, 3 minutes at 100OC. (212OF.), beans, 3 minutes a t 82OC. ( 180F.), carrots, 7 minutes a t 100OC. (212OF.), and potatoes, 5 minutes a t 100OC. (212OF.), the percentage losses respectively were: peas, 39% K,O (potassium oxide), 20% P,05 </p></li><li><p>66 FRANK A. LEE </p><p>(phosphorous pentoxide); beans, 40% K,O; carrots, 16% K,O, 15% P205; potatoes, 9% L O , 9% P,O,. </p><p>Calcium was found to be generally absorbed by the vegetables dur- ing blanching, the extent of the increase depending upon the nature of the vegetables, the hardness of the blanching water, and the time of blanching. </p><p>TABLE I Gain in Calcium Content during Blanching a </p><p>Calcium oxide content ( W ) Gain of calcium oxide </p><p>vegetables in vegetables Vegetable Water </p><p>Raw Blanched </p><p>Peas 0.0100 0,0199 0.0302 52 Beans 0.0087 0.104 0.124 19 Carrots 0.087 0.0432 0.0521 21 Potatoes 0.0087 0.0118 0.0157 33 </p><p>(1 Horner ( 19361937b). </p><p>Lee and Whitcombe (1945) studied the effects of the blanching of vegetables in various types of potable water. These authors, in confirma- tion of Horners findings, found that vegetables prepared for freezing preservation by blanching in hard water showed significant increases in the calcium content. They found also, that the blanching of vegetables in water containing one part per million of iron, resulted in no significant changes in the iron content of the peas and snap beans used in the experiments. </p><p>Kramer and Smith (1947) made a study of the effect of duration, temperature, and type of blanching on the mineral composition of peas, green beans, lima beans, and spinach for preservation by canning. Steam blanching was found to cause no significant change in the composition of any except spinach, where moderate losses were noted in the ash and phosphorus contents and slight gains noted in the calcium contents. For water blanch in general, the effect of time was more important than temperature, The mineral components showed changes as follows. The severest water blanch caused a reduction of 54% in the ash content of spinach. The calcium content of green beans was not affected by the water blanch, that of lima beans slightly increased, and that of peas and spinach increased by as much as 79 and 54%, respec- tively. The phosphorus content of spinach as reduced by as much as 40%. but rarely more than 10% for the other vegetables. </p><p>Data showing the effect of blanching on the mineral composition of </p></li><li><p>TABLE I1 Changes in Proximate and Mineral Composition of Canned Peas as a Result of Blanching, Fill-In Weight Basisa </p><p>Fancy grade, No. 4 sieve s u e Blanching Mineral composition </p><p>( "F. ) ( min. ) Moisture Protein Fat Fiber Ash Carbohydrate Calcium Phosphorus (mg./100 g.) </p><p>Type of blanch Temp. Time </p><p>None - - 82.19 5.04 0.36 1.86 0.56 9.99 19 63 Water 180 3 81.99 5.03 0.40 2.04 0.60 9.89 25 74 Water 180 6 82.65 4.82 0.37 2.09 0.54 9.53 30 61 Water 180 9 83.24 4.75 0.34 2.11 0.51 9.05 33 61 Water 190 3 82.22 4.94 0.40 2.11 0.56 9.77 29 65 Water 190 6 82.65 4.63 0.38 2.14 0.55 9.65 31 63 </p><p>Water 200 3 81.93 4.99 0.41 1.99 0.55 10.13 30 67 m td Water 200 6 83.04 4.76 0.38 1.92 0.56 9.34 32 65 F * 1: Water 200 9 83.76 4.46 0.35 1.93 0.55 8.95 34 62 Steam 210 1 81.14 5.42 0.38 2.06 0.61 10.39 22 70 n E 2: Steam 210 2 80.54 5.75 0.42 2.24 0.56 10.49 22 78 Steam 210 3 80.74 5.57 0.40 2.42 0.57 10.30 23 79 d </p><p>90.85 2.81 0.56 0.96 1.74 2.98 119 70 x None - - Water 170F 1 91.60 2.69 0.56 1.03 1.48 2.64 110 59 Water 170 4 92.63 2.47 0.56 1.04 1.21 2.09 137 49 Water 170 7 92.54 2.57 0.53 1.03 1.13 2.20 150 49 Water 185 1 92.37 2.63 0.51 0.86 1.31 2.32 141 50 Water 185 4 92.61 2.64 0.48 0.92 1.07 2.28 155 45 Water 185 7 93.00 2.61 0.42 0.92 0.98 2.07 144 49 Water 200 1 91.63 2.77 0.60 1.05 1.38 2.57 137 58 Water 200 4 92.61 2.66 0.52 1.10 0.92 2.19 153 42 Water 200 7 92.79 2.70 0.48 0.96 0.80 2.27 183 43 Steam 210 0.75 91.77 2.59 0.57 0.91 1.52 2.64 134 53 Steam 210 1.5 91.66 2.77 0.56 0.97 1.54 2.47 128 60 Steam 210 3 91.77 2.85 0.62 0.88 1.49 2.39 120 62 </p><p>Proximate composition (9) </p><p>Water 190 9 84.28 4.57 0.36 1.97 0.58 8.24 32 65 2 </p><p>Changes in Proximate and Mineral Composition of Spinach as a result of Blanching, Fill-In Weight Basis. </p><p>M v) v) </p><p>m 4 </p><p>aKramer and Smith (1947). </p></li><li><p>68 FRANK A. LEE </p><p>peas are presented in Table 11, along with data on other substances. Steam blanching reduced the moisture content by 1 to 2%. The corres- ponding small increases in all the components therefore indicate that there was little or no change in the mineral composition of peas as a result of steam blanching. </p><p>Regardless of temperature, the short water blanching period of 3 minutes caused a slight loss in moisture content. As the blanching time was increased, however, the moisture content increased with time and temperature until the 9-minute blanch at 93OC. ( 2 0 0 O F . ) resulted in a 1.57% increase in moisture for the fancy peas and the 12-minute blanch at 93OC. (200OF.) resulted in a 2.15% increase in the moisture of the standard peas. The increase in moisture content was compensated for by a decrease in ash and in other materials. Although considerable losses were recorded for the ash content, especially of the standard peas, the total ash content of about 0.5% did not influence materially the general proximate composition. </p><p>The calcium content increased rapidly with time and temperature of the water blanch, from 19 mg. for the unblanched to 34 mg. for 100 grams for the fancy peas blanched for 9 minutes at 93OC. (200F.), and from 33 mg. for the unblanched to 45 mg. per 100 grams for the standard peas bIanched for 12 minutes at 93OC. (200OF.). This is in agreement with Horner, and with Lee and Whitcornbe. </p><p>The phosphorus content was not materially affected by any of the blanching treatments, whereas Horner reported considerable loss in phosphorus content of peas as a result of blanching. </p><p>The loss of total ash components of peas was not due to losses in phosphorus, and certainly not to calcium, which was actually taken up from the blanching water, but to losses of other more soluble minerals, particularly potassium, which is present in comparatively large quantities. </p><p>Loss in total ash as a result of water blanch of spinach was also significant; the maximum reduction for the 7-minute blanch at 93OC. (200OF.) varied from 1.74% to 0.80% or more than a 50% loss. As with peas, the calcium content increased with increasing time and tempera- ture of the water blanch until the 7-minute blanch at 93OC. (200OF.) resulted in a calcium content of 183 mg. per 100 grams compared to 119 mg. per 100 grams for the unblanched sample. The phosphorus con- tent declined from 70 mg. for the unblanched sampIe to 43 mg. per 100 grams for the most severe water blanch (Table 11). </p><p>2. SUGARS AND PROTEINS Magoon and Culpepper (1924) found that considerable losses in </p><p>sugars and other soluble substances resulted when peas, snap beans, </p></li><li><p>TABLE 111 Analyses of Stringless Green Pod String Beans, before and after Treatmenta </p><p>Average components ( 8 ) </p><p>Treatment of material Alcohol Sugars Polysac- pento- Nitrogen </p><p>Soluble Insoluble Reducing Total as starch protein if any Moisture Solids charides as </p><p>reducing </p><p>No treatment 89.40 10.60 4.46 6.14 2.34 0 2.34 2.60 1.15 1.72 8 Treated 4 min. with </p><p>Treated 8 min. with </p><p>Scalded 4 min. in </p><p>E k </p><p>1.73 Q Scalded 4 min. in 8 </p><p>8 </p><p>89.60 10.40 4.38 6.02 2.39 0 2.39 2.58 - 1.71 live steam </p><p>live steam </p><p>boiling water 90.05 9.95 4.15 5.130 2.01 0 2.01 2.52 - 1.65 </p><p>boiling water, then chilled 30 sec. in m cold water 90.83 9.17 3.73 5.44 1.78 0 1.78 2.33 - 1.63 </p><p>89.52 10.48 4.38 6.09 2.28 0 2.28 2.63 - </p><p>0 </p><p>Scalded 8 min. in boiling: water 90.43 9.57 3.75 5.82 1.97 0 1.97 2.67 - 1.64 - </p><p>Scalded 8 min. in boiling water, then chilled 30 sec. in cold water 90.67 9.24 3.61 5.5:; 1.80 0 1.80 2.35 - 1.48 </p><p>a Magoon and Culpepper ( 1924). </p></li><li><p>70 FRANK A. LEE </p><p>and spinach were scalded in boiling water and chilled in cold water thereafter; for 2 minutes and 4 minutes in the case of spinach and peas, and 4 minutes and 8 minutes in the case of snap beans, in preparation for canning. </p><p>These authors concluded that the chilling step following scalding resulted in loss of nutrients. They further concluded in the case of spin- ach, peas, and snap...</p></li></ul>

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