Research on the variations in the volatile compound and vitamin content in space foods after storage on the TG-1 spacecraft

ABSTRACT

Maintaining the nutrients and flavor acceptability of space food is critical for long-term manned space flights. Five different space food items from one batch, including braised beef with potatoes, stewed duck with sauce, black tomato powder, tea seed oil and fish oil were launched on the TG-1 spacecraft, and then brought back to Earth by the SZ-9 and SZ-10 manned spaceships respectively. The same food items and materials as those sent into space were stored in an environmentally controlled chamber on Earth as controls. Variations in certain volatile compounds in both braised beef with potatoes and stewed duck with sauce were observed after space flight, but no notable differences were observed in the vitamin contents in black tomato powder, tea seed oil, or fish oil. More attention should be focused on volatile compounds variations, and measures should be taken to maintain food acceptability during storage in space.

RESUMEN

Cuando se realizan vuelos espaciales tripulados de larga duración, resulta crucial mantener los nutrientes y un sabor aceptable en los alimentos enviados al espacio. Para el presente estudio, se enviaron al espacio cinco alimentos espaciales distintos a bordo de la nave TG-1: carne de res estofada con papas, pato estofado con salsa, polvo de tomate negro, aceite de Camelia y aceite de pescado; los mismos regresaron a tierra en las naves espaciales tripuladas SZ-9 y SZ-10. A su vez, en una cámara de ambiente controlado en tierra se almacenaron como control los mismos alimentos y materiales enviados al espacio. Después del vuelo se constataron variaciones en ciertos compuestos volátiles presentes tanto en la carne de res estofada con papas como en el pato estofado con salsa, sin que se presentaran diferencias significativas en el contenido vitamínico del polvo de tomate negro, el aceite de Camelia o el aceite de pescado. A manera de conclusión, se recomienda prestar mayor atención a las variaciones de los compuestos volátiles e implementar medidas para mantener la aceptabilidad de los alimentos destinados a ser almacenados en el espacio.

PALABRAS CLAVE:

• Alimentos espaciales
• compuestos volátiles
• vitaminas
• cocina china
• paquete de papel aluminio

KEYWORDS:

• Space food
• volatile compounds
• vitamins
• Chinese cuisine
• aluminum foil package

1. Introduction

The environment in space is very different from the environment on Earth, and gamma rays, high-energy protons, and heavy ions from cosmic rays pose a great threat to nutrient stability. Nutrition is of critical concern for crewmembers served on long-term space flight missions, such as the Space Station, Lunar Station, and Mars Station, as body weight loss is a primary consequence of altered nutrition and insufficient nutrient supply, which is frequently observed during space flight (Convertino, 2002; Winitz, Graff, Gallagher, Narkin, & Seedman, 1965; Stein, 2001). The environmental factors in space are likely to cause changes in the flavor and vitamin content of food, and these changes may affect the nutritional value and sensory acceptability of space food, thus further affecting the health of astronauts(Lane, Smith, Rice, & Bourland, 1994).

Currently, space food is mostly pre-packaged and ready-to-eat (Sun, Tou, Yu, Girten, & Cohen, 2014). As human footsteps reach further into outer space, measures must be taken to maintain proper nutrition for crew members during long-term space flights, including how to maintain the nutrients and acceptability of foods, which is a major issue faced by space food scientists (Smith, Rice, Dlouhy, & Zwart, 2013). The United States performed space food nutrient assessment experiments during ISS missions for a period of 880 days, and even for three years (Cooper, Perchonok, & Douglas, 2017; Zwart, Kloeris, Perchonok, Braby, & Smith, 2009). The variations in the vitamin and amino acid contents of five foods and compound vitamin tablets were investigated during storage in earth orbit. Farming in space or on land away from the Earth will be considered due to launch capacity limitation (Bamsey et al., 2009; Jr & Brown, 2006; Monje, Stutte, Goins, Porterfield, & Bingham, 2003), which will provide crewmembers with fresh food such as cereals, fruits and vegetables.

Chinese cuisine is vacuum packaged and heat-stabilized to serve as space food, which is very popular among Chinese astronauts. It is possible that radiation from the space environment may degrade nutrients or even create off-flavors as a result of oxidation. We hypothesized that susceptible vitamins and flavor substances may be the first to degrade in space, since they are the first to degrade on Earth (Gamboa-Santos et al., 2014; Kong et al., 2017). An effective method for assessing flavor and nutrient stability in space is to perform experiments under real radiation exposure during the long-term storage conditions associated with long-term space flight. We therefore carried out this research with the objective of determining the stability of the vitamins and flavors in foods and food materials after long-term space flights on the TG-1 spacecraft.

2. Materials and methods

2.1. Chemicals and materials

Standards of riboflavin, nicotinic acid, nicotinamide, pantothenic acid, pyridoxine, pyridoxal, biotin, folic acid, cobalamin, ascorbic acid, and tocopherol (including the α, β, γ, and δ active forms) were purchased from Sigma. Ammonium acetate was HPLC grade, acetonitrile was HPLC grade, and ultra-pure water was obtained from a commercial ultrapure water instrument (Milli-Q Advantage A10).

The foods and food materials were selected based on the following criteria: a. currently used in the Shen Zhou space food system, b. a potential source of space food material, and c. representative of a typical type of space food (such as canned food, or a natural food rich in vitamins). The quantities of the foods and materials used in the study were limited by the volume and mass of the TG-1 spacecraft. Three foods were vacuum packaged in four-layer aluminum foil bags (PET/Al/PA/CPP) for the study, including braised beef with potatoes, stewed duck with sauce, and freeze-dried black tomato powder, with the former two were sterilized to make the product thermal stable. The tea seed oil and fish oil were packaged in three-layer aluminum foil bags (PET/Al/CPP) without vacuum packaging. All food items and materials were obtained from the same batch production from the same manufacturer to ensure that the samples were homogeneous. It should be pointed out that since the place in the spaceships is limited, only one batch has been taken into space and then was analyzed, so the differences between batches were not properly taking into account.

Two identical retardant cloth bags (Beijing Leather Factory, Beijing, China) were prepared at the Astronaut Center of China, with two replicates of the previously mentioned food items and materials from a single batch based on the limited experimental item load of the spacecraft, and the differences between batches is eliminated (Wu, Sun, Zhang, Shen, & Weng, 2016). The two bags were launched on the TG-1 spacecraft in September 2011, and were brought back to Earth 274 days and 636 days later on the TG-1 spacecraft flights by SZ-9 and SZ-10 manned space flight missions, respectively, as shown in Table 1. Due to the limited flight load on the manned spaceships, only a limited amount of the research samples without repetitions was brought back by the crewmembers during the space flight missions from the TG-1 spacecraft.

Table 1. Food samples information.

Tabla 1. Información sobre las muestras de alimentos.

No.	Food item	Net weight/g	Duration in orbit/days
1	Braised beef with potatoes	90	274
2	Stewed duck with sauce	90	636
3	Freeze-dried black tomato powder	5.5	274
4	Fish oil	5.5	274
5	Tea seed oil	5.5	274

2.2. Volatile compound analysis

The volatile compounds in the four kinds of canned food were extracted using the SPME method. The needle for SPME was CAR/PDMS (75 μm). A homogenous sample (6 g) was placed into the solid phase microextraction vial, and 1 μL of 2-methyl-3-heptanone (1.632 μg/μL) was added as an internal standard. The sample was equilibrated at 50°C for 30 min, and then the SPME needle was inserted, and the sample was adsorbed for 40 min, and then analyzed by a Sniffer 9000 sniffing instrument coupled with a Agilent 7890A −7000B GC-MS. After the compound was detected by mass spectrometry and identified by a search of the NIST2.0 library with MS interpreter after retention index calibration, a quantitative analysis was conducted by calculating the peak area (Baker et al., 2003; Dionísio, Gomes, & Oetterer, 2009; Keast & Lau, 2006).

2.3. Vitamin analysis

Based on the nutritional properties of certain food samples launched and that of concern for spaceflight and especially for long-term duration spaceflight such as space station and residence in Lunar base missions, the contents of 10 water-soluble vitamins, including thiamine, riboflavin, niacin, niacinamide, pantothenic acid, pyridoxine, topiramate pyridoxal, biotin, folic acid, and cobalamin in freeze-dried black tomato powder were determined by LC-MS-MS method, as described previously (Chen & Wolf, 2007; Gratacos-Cubarsi, Sarraga, Clariana, Regueiro, & Castellari, 2011; Holler, Wachter, Wehrli, & Fizet, 2006; Schimpf, Spiegel, Thompson, & Dowell, 2012) using a Acquity UPLC and Xevo TQ ultra-performance liquid chromatography-tandem mass spectrometry. The vitamin C content of the freeze-dried black tomato powder and the tocopherol content in fish oil and tea seed oil was assessed according to a previously reported method (Gimeno, Castellote, Lamuelaraventã3s, Torre, & Lã3pezsabater, 2000; Lykkesfeldt, 2000) using a Hitachi L-2000 liquid chromatography, and the quantitative analysis was conducted by calculating the peak area.

3. Results and discussion

3.1. Volatile compound variation

Samples of braised beef with potatoes and stewed duck with sauce were launched on the TG-1 spacecraft and brought back by the SZ-10 mission after storage in orbit for 636 days. The volatile compound analysis was conducted six days after return to earth. The total ion current charts of the volatile compounds are shown in Figures 1 and 2, and the identified flavor compounds are shown in Tables 2 and 3.

Table 2. Flavor substance content variation of braised beef with potatoes.

Tabla 2. Variación en el contenido de sustancias de sabor de la carne de res estofada con papas.

No.	Compounds	Samples brought back by SZ-10 mission/%	Ground control samples/%
1	Spathulenol	20.3	27.6
2	2-butyl 4-ethylbenzoate	13.5	12.3
3	Ethyl acetate	9.2	2.1
4	6-methyl-5-hepten-2-one	7.2	7.4
5	Anethole	6.7	7.5
6	α- Hydrophyllene	5.3	4.6
7	α- Pinene	5.0	6.0
8	Camphene	4.9	4.8
9	4-terpineol	4.3	5.2
10	Curcumin	3.6	2.4
11	Cypressene	3.3	1.3
12	Benzaldehyde	3.3	2.3
13	Linalool	3.1	3.3
14	α- Terpineol	3.1	3.1
15	Acetic acid	2.1	1.8
16	Isopulegol	1.5	4.0
17	Nonanal	1.3	0.6
18	D-limonene	1.1	2.8
19	2-furanemethanol	1.0	0.6
20	3-methyl-4-hydroxybenzaldehyde	0.2	0.1

Table 3. Variation of flavor substances of stewed duck with sauce.

Tabla 3. Variación en las sustancias de sabor del pato estofado con salsa.

No.	Compounds	Samples brought back by SZ-10 mission/%	Ground control samples/%
1	2-Pentylfuran	32.9	29.2
2	Ethyl acetate	10.7	10.0
3	2-ethylfuran	7.1	2.6
4	2-butyl 4-ethylbenzoate	6.9	7.1
5	1-octen-3-ol	5.7	5.8
6	Spathulenol	5.5	2.7
7	Camphene	5.0	5.4
8	Benzaldehyde	4.5	5.0
9	2-(1-pentenyl)-furan	3.6	2.1
10	α- Curcumin	2.9	3.1
11	Furfural	2.2	3.2
12	α- Cypressene	2.2	3.3
13	Hexanol	2.0	5.2
14	Gingerene	1.5	0.1
15	Anethole	1.5	1.2
16	D- Limonene	1.4	1.8
17	Hexanal	1.4	7.6
18	Thujopsene	1.3	0.7
19	6-methyl-5-hepten-2-one	1.1	2.7
20	2-furanemethanol	0.6	1.3

Figure 1. The total ion current of flavor substances in the stewed duck with sauce (flight sample and ground control sample from left to right).

Figura 1. Corriente iónica total de las sustancias de sabor en el pato estofado con salsa (muestra enviada al espacio y muestra de control en tierra, de izquierda a derecha).

Figure 2. The total ion current of flavor substances in the braised beef with potatoes (flight sample and ground control sample from left to right).

Figura 2. Corriente iónica total de las sustancia de sabor en la carne de res estofada con papas (muestra enviada al espacio y muestra de control en tierra, de izquierda a derecha).

As shown in Table 2, the major volatile compounds in the braised beef with potatoes sample were spathulenol, 2-butyl 4-ethylbenzoate, ethyl acetate, 6-methyl-5-hepten-2-one, and anethole. The compounds that contribute to the flavor of braised beef with potatoes are mainly aliphatic alcohols, esters, ketones, and alkenes, and have fewer irritating aldehyde flavor substances. The flavor ingredients found in braised beef with potatoes may have come from the food material, spices or compounds generated during processing. After storage, there was little variation in the volatile compounds, including higher relative levels of spathulenol, 6-methyl-5-hepten-2-one, anethole, α-pinene, 4-terpineol, linalool, isopulegol, and d-limonene in the ground control samples and higher levels of 2-butyl 4-ethylbenzoate, ethyl acetate, α-hydrophyllene, camphene, α- curcumin, α-cypressene, benzaldehyde, acetic acid, nonanal, 2-furanemethanol, and 3-methyl-4-hydroxybenzaldehyde in the space flight samples. The volatile compounds increased in the ground control samples mainly consisted of enols.

As shown in Table 3, the main volatile compounds in the stewed duck with sauce samples were 2-pentylfuran, ethyl acetate, 2-ethylfuran, 2-butyl 4-ethylbenzoate, and 1-octen-3-ol. The compounds that contribute to the flavor of stewed duck with sauce are mainly furans, esters, and aliphatic alcohols; and it has few irritating aldehyde flavor substances. After storage for nine months, there were slight, but not significant variations in several volatile compounds, including 2-pentylfuran and ethyl acetate, as well as higher levels of 2-ethylfuran, spathulenol, 2-(1-pentenyl)-furan, gingerene, anethole, and thujopsene in space flight samples, and higher levels of 2-butyl 4-ethylbenzoate, 1-octen-3-ol, camphene, benzaldehyde, α-curcumin, furfural, α-cypressene, hexanol, d-limonene, hexanal, 6-methyl-5-hepten-2-one, and 2-furanemethanol in the ground control samples.

The different canned foods had different volatile compounds compositions, which were derived from the food ingredients and condiments added during processing and contributed to their unique flavor.

3.2. Variations in vitamins

3.2.1. Natural vitamins in freeze-dried black tomato powder

The standard curves of each vitamin are shown in Table 4. The correlation coefficients (R values) of the standard curves were greater than 0.996, and thus could be used to determine the concentrations in the test samples. Vitamin contents in the ground control and space flight freeze-dried black tomato powder samples are shown in Table 5.

Table 4. Standard curves used for each vitamin analysis.

Tabla 4. Curvas estándar utilizadas para cada uno de los análisis de vitaminas.

No.	Vitamins	Standard curve^a	Correlation coefficient
1	Biotin	y = 1027.4x-152.52	0.9999
2	Vitamin B12	y = 483.85x-187.48	0.9990
3	Folic acid	y = 42.51x-5.01	0.9998
4	Niacin	y = 36.23x-2.37	0.9989
5	Pantothenic	y = 324.41x + 17.16	0.9999
6	Pyridoxal	y = 4891.9x + 1620.6	0.9997
7	Riboflavin	y = 524.01x + 7.10	0.9999
8	Thiamine	y = 13915x + 9471.4	0.9995
9	Vitamin C	y = 2.04x + 1.5	0.9966
10	α- tocopherol	y = 21000x-19336	0.9991
11	(β + γ) – tocopherol	y = 44668x + 14643	0.9996
12	δ- tocopherol	y = 34191x-56606	0.9969

a: y indicates peak area, x indicates concentrations of vitamins (ng/mL).

y indica el área pico, x indica la concentración de vitaminas (ng/mL).

Table 5. Content of vitamins for freeze-dried black tomato powder.

Tabla 5. Contenido de vitaminas en el polvo de tomate negro liofilizado.

No.	Vitamins	Ground control samples	Samples brought back by SZ-9 mission
1	Biotin (μg/100g)	3.96	3.82
2	Vitamin B12 (μg/100g)	<0.1	<0.1
3	Folic acid (μg/100g)	<0.2	<0.2
4	Niacin (mg/100g)	3.75	3.53
5	Pantothenic (μg/100g)	418	409
6	Pyridoxal (μg/100g)	347	333
7	Riboflavin (μg/100g)	14.2	16.5
8	Thiamine (μg/100g)	162	163
9	Vitamin C (mg/100g)	292.8	287.0

As shown in Table 5, vitamin B₁₂ and folic acid were not detected in either the ground control and space flight samples, and no notable variations were observed in the concentrations of biotin, niacin, pantothenic, pyridoxal, vitamin C, riboflavin, and thiamine between the space flight and ground control samples. Freeze-dried black tomato powder is rich in natural water soluble vitamins, which can be developed as a nutrient supplement or rehydration drink without deep processing, to serve as a routine supply of water-soluble vitamins in the space diet.

3.2.2. Tocopherol variation in tea seed oil and fish oil

The standard curve for tocopherol is shown in Table 4. In this table, the tocopherol standard curve correlation coefficient (R²) was 0.996 or greater, and therefore could be used for the analysis of tocopherol contents.

The tocopherol contents of tea seed oil and fish oil are shown in Table 6. As shown in Table 6, the tocopherols in tea seed oil were mainly the α-tocopherol type, with small amounts of the other three types of tocopherol. The tocopherol in fish oil is mainly the (β + γ)-tocopherol type, followed by the α-tocopherol and δ-tocopherol types. Compared with the ground control samples, the tocopherol levels in the space flight samples were slightly lower. Compound application of tea seed oil and fish oil can be a better natural vitamin E source to provide different types of tocopherol for astronaut during spaceflight missions .

Table 6. Tocopherol content of tea seed oil and fish oil samples.

Tabla 6. Contenido de tocoferol en las muestras de aceite de Camelia y aceite de pescado.

No.	Food item	Tocopherol	Ground control samples (mg/100g)	Samples brought back by SZ-9 mg/100g
1	Tea seed oil	α-tocopherol	13.4	12.9
		(β + γ) -tocopherol	1.1	0.7
		δ-tocopherol	0.6	0.4
2		Total	15.1	14.0
3	Fish oil	α-tocopherol	19.8	17.9
		(β + γ) -tocopherol	34.8	30.6
		δ-tocopherol	19.2	17.7
4		Total	73.8	66.2

Flavor and nutrition as vitamins are two important attributes of space foods. Vitamins are closely related to the health of astronauts during long term space flight. Changes in the volatile compound contents directly affect the sensory acceptance of space foods, which in turn affects the astronauts’ food intake. Compared to other nutrients in foods, such as proteins, fats, carbohydrates, and minerals, vitamins are more environmentally susceptible, more easily degraded, and undergo structural changes under certain conditions encountered during processing or storage, such as heat, oxidation, and radiation (Dionísio et al., 2009; Jeong et al., 2017; Leskova et al., 2006). In this study, water-soluble vitamins and vitamin E (a fat-soluble vitamin) were selected as representative indicators. The samples were packed in aluminum foil bags, which have excellent oxygen and moisture barrier properties. Because of the absence of protection by the atmosphere, the radiation levels in space are higher than those on the surface of Earth. However, because of the physical radiation shielding of the manned spacecraft, the radiation level inside the cabin is greatly reduced compared with that outside (Shinn, Nealy, Townsend, Wilson, & Wood, 1994). As enols, a type of volatile compound, are mainly small molecules that are more sensitive to radiation or oxidation than vitamins, protective measures should be taken to offset their reduction or variation. Various aspects of the space environment, including vibrations, noise, microgravity, and electromagnetic radiation, may significantly affect the human body but have little effect on the properties of well-packed food items. The results of this study are consistent with other results reported in the literature (Zwart et al., 2009). In contrast to the unique weightlessness conditions in space, other environmental conditions that could affect the physical and chemical properties of foods, such as temperature and humidity, were the same as those on the ground. However, the radiation levels in spacecraft are higher, which may harm the more sensitive flavor substances (Townsend, 2005). The mechanism underlying these related changes is unclear, and should be examined in a subsequent study.

4. Conclusion

Variations of the volatile compounds in traditional Chinese canned food items and vitamins in natural food ingredients were investigated after storage on the TG-1 spacecraft. Since independent packaged samples assignment was not enough, which did not take batches and repetitions into account because of the space limitation of the manned spaceship, making further statistical analysis of the results impossible. However, based on available data, it is reasonable to assume that compared with the ground control samples, some of the trace alkene-type volatile compounds were decreased in both braised beef with potatoes and stewed duck with sauce after 274 and 636 days of space flight, respectively. Our findings on volatile changes between the ground control and flight saples give references in programming future ground-based experiment or real spaceflight missions, to help preserve the flavor property of space food and sensory acceptance for crewmembers. The vitamin analysis showed that, compared with the ground control samples, the vitamin content of the space flight samples of freeze-dried black tomato powder did not differ. The types of tocopherols present in fish oil and tea seed oil were different, which could be serve as a natural tocopherols admixture by combined application; however, no notable difference was observed between the ground control and space flight samples.

Acknowledgments

This study was supported by grants from the Space Medicine Fundamentals and Application Foundation (SYFD150111808, SMFA16B02). We thank the crewmembers of the SZ-9 and SZ-10 space flight missions for bringing back our samples.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Space Medicine Fundamentals and Application Foundation [SYFD150111808, SMFA16B02].