Oil-water Separation of Mayonnaises and Semisolid Dressings by Freezing and Thawing

Abstract

Mayonnaises and dressings are preferred seasonings, and a variety of such products are available on the market. Six mayonnaises, three salad creamy dressings, one oil-in-water (O/W) type semisolid dressing, and one water-in-oil-in-water (W/O/W) type semisolid dressing, all of which are commercially available, were frozen at −20 °C, −23 °C, −25 °C, −28 °C, and −80 °C for specified time periods and then thawed at about 25 °C. The changes in temperature of the mayonnaises and dressings during freezing and thawing depended on their types. Oil-water separation was observed after thawing for all mayonnaises, except when rapidly frozen at −80 °C. Up to 60% of the oil phase contained in the dressings separated after thawing, suggesting that thickeners added to the aqueous phase partially suppressed the oil-water separation. The temperature changes and oil-water separation behaviors of the W/O/W type semisolid dressing were similar to those of the mayonnaises.

Introduction

Seasonings such as mayonnaises and dressings are now commonly consumed together with fresh vegetables in Japan, due to the Westernization of eating habits (Kawano, 1983). Mayonnaise and dressing are strictly defined in Japan by the Japanese Agricultural Standard (JAS). A semisolid dressing is an O/W emulsion type seasoning which contains edible vegetable oil and other ingredients, with a viscosity of 30 Pa·s or more, and is mainly used for salads. Among semisolid dressings, any dressing containing egg yolk or whole egg, with no more than 30 wt% of water, and at least 65 wt% of edible vegetable oil and other specified ingredients, is defined as a mayonnaise. The oil droplets in the mayonnaise have an irregular shape because of the high proportion and dense packing of the oil phase (Depree and Savage, 2001). Other dressings which appear similar to mayonnaise, and with similar viscosity values, but in which the contents of edible vegetable oil and other ingredients do not meet the mayonnaise standards, are classified as salad creamy dressings or semisolid dressings. The proportion of edible vegetable oil in salad creamy dressings and semisolid dressings should be between 10–50%, and 10% or more, respectively, while the water content in both types of dressings should be 85 wt% or less. Although these dressings have a low oil content, their viscosities are similar to that of mayonnaise because they contain substances that have thickening effects, such as starch and paste.

Consumers' demand for food has recently diversified. Dressings for people who do not eat animal foods such as eggs, honey, milk etc. are commercially available in Japan. A W/O/W emulsion type dressing, which contains small water droplets inside the oil droplets, is claimed by the manufacturer to be designed to reduce calories and is also commercially available.

Since smooth textures and palatability are characteristic features of mayonnaises and dressings, it is necessary to understand their flow properties. Furthermore, it is important to investigate the changes in these properties during their distribution and storage. The development of freezing technology has facilitated the preservation of products for long periods and thus enabled the distribution of frozen foods. However, O/W emulsion type foods such as mayonnaises and dressings typically exhibit oil-water separation after freezing and thawing, which significantly impairs the product value. The oil-water separation due to freezing and thawing needs to be suppressed in order to improve the stability of the emulsion. However, its mechanism has not been elucidated to date (Shariful et al., 2018; Ueno, 2016). To our knowledge, there seem to be fewer studies on the oil-water separation in semisolid dressings, as compared to that in mayonnaises.

The purpose of this study is to investigate the oil-water separation, after freezing and thawing, for several commercially available mayonnaises and dressings.

Materials and Methods

Materials    Mayonnaises used were Kewpie Mayonnaise (Kewpie, Tokyo Japan; designated as mayonnaise A), Kewpie Linseed Oil Mayonnaise (Kewpie; mayonnaise B), Egoma Ichiban Mayonnaise (Sokensha, Yokohama Japan; mayonnaise C), Matsuda Mayonnaise (sweet type; Nanakusa-no-sato, Saitama Japan; mayonnaise D), SSK Mayonnaise (SSK Foods, Shizuoka Japan; mayonnaise E) and Pure Select Mayonnaise (Ajinomoto, Tokyo Japan; mayonnaise F). Mayonnaise C contains oil extracted from egoma (Perilla frutescens) seeds. Egoma, a plant native to Southeast Asia, is an annual herb that belongs to the mint family. The oil present in egoma seeds is rich in polyunsaturated fatty acids. Its major component is α-linolenic acid, followed by oleic and linoleic acids (Kurata et al., 2005). Dressings used were Kewpie Half (Kewpie; dressing G), Kewpie Zero Non-Cholesterol (Kewpie; dressing H), Kewpie Light 80% Calorie Cut (Kewpie; dressing I), SSK Calorie Half (SSK Foods; dressing J), and Pure Select Kokuuma 65% Calorie Cut (Ajinomoto, dressing K). Dressings G, H, and I are classified as salad creamy dressings, while dressings J and K are classified as semisolid dressings. Dressing K is a W/O/W emulsion, whereas all the other mayonnaises and dressings are O/W emulsions. Table 1 shows the nutrient compositions of all the mayonnaises and dressings investigated in the present study, which are based on the nutritional information on the product labels.

Table 1. Ingredients and nutritional contents of mayonnaises and semisolid dressings.

	Mayonnaise						Dressing
JAS*1	Mayonnaise						Salad creamy dressing			Semisolid dressing
	A	B	C	D	E	F	G	H	I	J	K
Ingredients*2	vegetable oil	vegetable oil	vegetable oil	rapeseed oil	vegetable oil	vegetable oil	vegetable oil	vegetable oil	vinegar	vegetable oil	vegetable oil
	egg yolk	(rapeseed oil, linseed	(egoma oil, safflower	egg	vinegar	(rapeseed oil,	egg	vinegar	egg	egg yolk	(rapeseed oil,
	vinegar	oil, soybean oil)	oil, rapeseed oil)	vinegar	egg	soybean oil, corn oil)	vinegar	egg	vegetable oil	starch syrup	corn oil)
	dietary salt	vinegar	egg yolk	dietary salt	dietary salt	egg	dietary salt	dietary salt	dietary salt	dietary salt	egg
	spice	egg yolk	vinegar	honey	sugar	starch syrup	sugar	starch syrup	dextrin	thickner	dietary sak
	condiment	dietary salt	sugar	mustard	spice	vinegar	spice	sugar	saccharide	sugar	vinegar
	(aminoacid)	sugar	dietary salt	garlic	condiment	dietary salt	protein-hydrolyzate	protein-hydrolyzate	protein-hydrolizate	powdered-egg	sugar
	spice extract	protein-hydrolyzate	spice	pepper	(amino acid)	spice	thickener	spice	spice	yolk	lemon juice
		spice		ginger		lemon juice	(xanthan gum)	thickner	flavored oil	condiment	protein-
		condiment				condiment	condiment	(xanthan gum, guar	thickner	(amino acid)	hydrolizate
		(amino acid)				(amino acid)	(amino acid)	gum)	(xanthan gum,	spice extract	glycine
		spice extract					spice extract	condiment	modified starch)		emulsifier
								(amino acid)	condiment		condiment
								spice extract	(amino acid)		(amino acid)
									sweetner		thickner
									(stevia)		acidifier
									spice extract		spice extract
											pigement
Energy (kcal)*3	100	100	104	105	108	110	49	50	20	50	36
Protein(g)*3	0.4	0.3	0.3	0.3	0.27	0.21	0.4	0.3	0.4	0.3	0.47
Lipid(g)*3	11.2	12	11.2	11.4	11.7	11	5.1	5.2	1.5	5	3.5
Carbohydrate(g)*3	0.1	0.1	0.4	0.18	0.24	0.54	0.3	0.4	0.9	0.9	0.48
Sdium chloride	0.3	0.2	0.28	0.21		0.27	0.4	0.4	0.5	0.4	0.7
equivalent (mg)*3

*1  Japanese Agricultural Standard

*2  From top to bottom in descending order of content

*3  per 15 g

Temperature measurement    About 10 mL of mayonnaise or dressing was added into a 15 mL conical tube using a syringe and a silicone tube. A thermocouple was inserted and fixed to the center of the sample from the lid of the tube through a hole. The tube was placed in the perforated polystyrene foam. Each sample was stored in a freezer (GX- 823HC, As One, Osaka) for about three days at −20 °C and for 24 to 36 h at −23 °C, −25 °C, and −28 °C. Each sample was also stored at −80 °C in a deep freezer for 3 h (VT-208HC, Nihon Freezer, Tokyo Japan). These temperatures represent the freezer settings, and the actual temperatures were measured with a calibrated thermometer. The accuracy in temperature control of freezer VT-208HC was set temperature ± ca. 1.2 °C. For convenience, the temperature is expressed as the freezer setting in the text. After the predetermined period, the sample was removed from the freezer and thawed at room temperature (about 25 °C). The sample temperature during freezing and thawing was recorded using a digital data logger (ADL12, As One).

Separation rate of oil    About 10 mL of mayonnaise or dressing was placed in a 15 mL conical tube, and centrifuged at 2 000 g for 60 min. The volumes of the water, emulsion, and oil layers of the sample were calculated from their heights after centrifugation. A layer with a mayonnaise-like appearance, located between the separated oil and water layers, is referred to as an emulsion layer. No oil-water separation was observed after centrifugation at 2 000 g for 60 min for all the samples without freezing and thawing.

Results and Discussion

Temperature change during freezing and thawing    The mayonnaises and dressings were stored at −20 °C, −23 °C, −25 °C, −28 °C, and −80 °C for predetermined periods, and then thawed at room temperature. The sample temperature was recorded both during freezing and thawing. Figure 1 shows the temperature changes observed for mayonnaise F, as well as for dressings I and J, as representative examples. A sharp rise in temperature was observed in the range of −5 to −16 °C as the sample temperature decreased. This is ascribed to the cancellation of the supercooling of the aqueous phase (Miyagawa et al., 2016; Katsuki et al., 2017a). The time at which the temperature started to decrease again, after the cancellation of the supercooling, was longer for dressing J (Fig. 1(c)) than for mayonnaise F (Fig. 1(a)). It was found that such times were longer for the dressings than for the mayonnaises, and is attributed to the higher water content of the dressings, as compared to that of the mayonnaises. The samples stored at −20 °C, −23 °C, −25 °C, and −28 °C showed a broad rise in temperature after a certain period elapsed at the predetermined storage temperature (Figs. 1(a) and (c)). For all the samples placed in the freezer set at −80 °C, a rise in temperature was observed during the cooling process. This is due to the heat generation associated with the crystallization of the oil phase in mayonnaises and dressings (Katsuki et al., 2017a; Miyagawa et al., 2016). The time at which this occurred was not always earlier for the sample stored at the lower temperature. This phenomenon is commonly observed for some vegetable oils in the bulk state (Miyagawa et al., 2015; 2019). Only dressing I exhibited no such heat generation (Fig. 1(b)), indicating that the vegetable oil present in the dressing did not crystallize, or that the generated heat was not perceptible due to very little crystallized oil.

Fig. 1.

Temperature changes of (a) mayonnaise F, (b) salad creamy dressing I, (c) semisolid dressing J during freezing process. Freezer settings: —; −20 °C, ⋯·; −23 °C, —; −25 °C, — · —; −28 °C. The inset shows the temperature changes of the samples stored at −80 °C.

Changes in sample temperature were also measured during the thawing process. Figure 2 shows the temperature changes during the thawing process of the samples frozen at −25 °C. When the temperature rose to about −10 °C, the rate at which the temperature increased slowed down for all the samples. This is attributed to the latent heat associated with the melting of the aqueous phase (Katsuki et al., 2017b). The rate at which the temperature rose, until the aqueous phase started to melt, tended to be smaller for mayonnaises than for dressings. The melting points of the vegetable oils that form the oil phase in mayonnaises, such as rapeseed oil and soybean oil, are about the same as that of water, or lower (Miyagawa et al., 2016). Therefore, the initial rise in temperature is considered to include the endothermic effect associated with the melting of the oil phase. Since mayonnaises have higher proportions of oil content than dressings, this effect will be more pronounced in mayonnaises, leading to lower rates of temperature increase, as compared to those observed for dressings. Similar tendencies were observed for mayonnaises and dressings frozen at other temperatures.

Fig. 2.

Temperature changes of samples frozen at −25 °C during thawing processes. Labels A to K correspond to the sample names listed in Table 1.

The time taken for the aqueous phase to melt reflects the proportion of the aqueous phase in the emulsion (Katsuki et al., 2017b). The melting time of the aqueous phase was shorter for mayonnaises than that for dressings. Figure 3 shows the relationship between the melting time of the aqueous phase and the energy (in kilocalories) per 15 g of mayonnaise or dressing, which is shown in Table 1, frozen at −20 °C, −23 °C, −25 °C, −28 °C, or −80 °C. The smaller the energy per 15 g of sample, the longer it took to melt the aqueous phase. This is consistent with the fact that mayonnaises have a higher percentage of oil content (and a correspondingly smaller aqueous phase) than do dressings. However, the melting time of dressing K was similar to those of the mayonnaises. This can be rationalized as follows. Dressing K is a W/O/W emulsion. Therefore, although the proportion of the external aqueous phase and the oil-droplet size are similar to those in the mayonnaises, the actual oil content in the dressing is significantly smaller than that in other dressings or mayonnaises. Because the size of the oil droplets in a mayonnaise is about a few micrometers, the size of the inner aqueous phase in the oil droplets of dressing K is estimated to be of the order of submicrons. The crystallization temperature of small water droplets has been reported to be significantly lower than that of bulk water (Walstra, 2002). The water in the inner aqueous phase is less likely to crystallize than that in the outer aqueous phase. The temperature rise due to the crystallization of the aqueous phase was observed only once for dressing K, suggesting that the inner aqueous phase of dressing K had not crystallized. Because only the external aqueous phase was melted, it is speculated that the melting time for dressing K is similar to that for the mayonnaises.

Fig. 3.

Relationships between the melting time of the aqueous phase and calories of the samples. Symbols: ○, mayonnaise A; ◊, mayonnaise B; □, mayonnaise C; △, mayonnaise D; ▽, mayonnaise E; ▷, mayonnaise F; ●, dressing G; ◆, dressing H; ■, dressing I; ▴, dressing J; ▼, dressing K.

The rate at which the temperature of the sample increases, after the melting of the aqueous phase, reflects the specific heat of the melted sample. This rate was found to be lower for dressings, as compared to that for mayonnaises, and can be ascribed to the fact that oil has a lower specific heat than water. In addition, it may be considered that the aqueous phase of dressings contains more components than that of mayonnaises. Only dressing H did not exhibit a sharp transition between the end of the melting of the aqueous phase and the subsequent rise in temperature after the melting (Fig. 2). Samples of dressing H, frozen at other temperatures, also exhibited similar blurred boundaries. Although the explicit reason for this is unknown, it is possible that dressing H may contain substances that melt around 0 °C.

Oil-water separation after freezing and thawing    Figure 4 shows the oil-water separation of all the mayonnaises and dressings, which were frozen at −20 °C, −23 °C, −25 °C, −28 °C, or −80 °C and then thawed at room temperature. For all samples, no oil-water separation occurred when it was thawed before the oil phase crystallized. This fact is consistent with the previous results on the freezing-thawing behavior of mayonnaise (Miyagawa et al., 2016). Dressing I exhibited no oil-water separation and no heat-generation of oil phase. Therefore, it is supposed that the oil phase of dressing I did not crystallize at any storage temperature. Mayonnaise F suppressed the oil-water separation only when it was frozen at −80 °C (Fig. 4). This is consistent with previous studies where it has been reported that the oil-water separation does not occur when the mayonnaise is rapidly frozen (Cornacchia and Roos, 2011; Vanapalli et al., 2002). For dressing K frozen at −80 °C, the emulsion and water layers were observed, but there was no separate oil layer. We propose that the destabilization of the W/O/W emulsion by freezing and thawing could exhibit the same trends as that of the O/W emulsion, when the inner aqueous phase of the W/O/W emulsion was not frozen, which would explain our observation for dressing K.

Fig. 4.

Volumetric fractions of oil, emulsion, and water layers of mayonnaises and dressings after their freezing and thawing. Labels A to K indicate the names of mayonnaises and dressings as listed in Table 1. The figures show the results for the samples frozen at the freezer settings of −20 °C, −23 °C, −25 °C, −28 °C, and −80 °C in order from top to bottom.

Except for mayonnaise F frozen at −80 °C, all the other mayonnaises were separated into three layers, oil, emulsion and water layers, after freezing and thawing, with the volumetric fraction of the oil layer being 60% or more. The salad creamy dressings were separated into two layers, the oil and emulsion layers, after freezing and thawing, and no water layer was observed. Also, the volumetric fraction of the oil layer was 10% or less. The volumetric fraction of the oil layer separated in the case of semisolid dressings was between those for the oil layers corresponding to the mayonnaises and salad creamy dressings. The oil content is different for mayonnaise, salad creamy dressing and semisolid dressing. The ratio of the fraction of the separated oil to that of the total oil content in the sample was estimated (Fig. 5). Since the oil contained in the sample can be considered to be in the oil phase, the lipid contained per 15 g sample (see Table 1) was regarded as the oil content. The density of the oil phase was assumed to be 0.92 g/cm³. The ratio of the separated oil was close to 1 for all the mayonnaises in the present study, except for mayonnaise F when frozen at −80 °C. As described above, no oil layer was observed for dressing I, which had the lowest oil content because the oil phase did not crystallize. The ratio of separated oil was in the range of 0–60% for all the other dressings. This suggests that dressings are more difficult to separate than mayonnaises. On the other hand, our previous study showed that the oil phase was almost completely separated when the O/W emulsion with an oil content of 30 wt% was stored at −20 °C to −28 °C and then thawed (Katsuki et al., 2017a). We proposed that the oil-water separation could be affected by factors other than the proportion of oil content in the emulsion. As mentioned before, the dressings typically contain thickeners. Also, increasing the viscosity of the aqueous phase is known to be an effective way to suppress the coalescence of oil droplets (McClements, 2007). It is presumed that the oil-water separation in dressing I was suppressed after freezing and thawing, because the aqueous phase of this dressing was highly viscous and partly gelled. Therefore, we suggest that the oil content of an emulsion does not affect its stability during freezing and thawing.

Fig. 5.

Relationship between the oil content of samples and the volumetric ratio of separated oil for the samples frozen at the freezer settings of −20 °C, −23 °C, −25 °C, −28 °C, and −80 °C. The symbols are the same as in Fig. 3.

Conclusions

The mayonnaises and dressings, i.e., salad creamy dressings and semisolid dressings, were frozen at −20 °C, −23 °C, −25 °C, −28 °C, and −80 °C for predetermined periods and then thawed at room temperature. The temperature changes of mayonnaises and dressings during freezing and thawing reflected the differences in the compositions of these emulsions. After freezing and thawing, the mayonnaises almost completely separated into oil and water layers, whereas the fraction of separated oil in the case of the dressings was 60% or less. We have suggested that the thickeners present in the aqueous phase of dressings suppressed the oil-water separation. The oil content of emulsions was considered to have essentially no effect on their stability during freezing and thawing. It was also suggested that the destabilization behavior of a W/O/W emulsion type dressing after freezing and thawing would be similar to that of O/W emulsion type mayonnaises.

Acknowledgements    This study was supported by Grant-in-Aid for JSPS Fellows, vide Grant No. JSPS KAKENHI (JP18J01966). We thank Mr. Enobi and Mr. Hayami for their technical assistance.

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