Dynamics of micronutrients of fresh and stale tomatoes (lycopersicum esculentum) sold within Umuahia metropolis in Nigeria as a function of handling practices

Abstract

Tomatoes are soft tissue perishable fruits high susceptible to bruises during loading, transportation, unloading, and retailing which lead to their deterioration and nutrient losses. This study explored the micronutrient changes in the fresh (whole) and stale (nkuwa) tomatoes during loading, transportation, unloading, distribution and retail sales in the three major retail market outlets in Umuahia metropolis with standard methods of analyses. The results of micronutrients (pro-vitamin A, vitamins B1, B2, B3 and C, calcium, magnesium, potassium, zinc, sodium and iron) evaluated revealed significant (p < 0.05) decrease for the entire stale tomato samples compared to their whole counterparts. With increase in distance from the landing bay, pro-vitamin A (β carotene) (598.36–579.64 µg/100 g), B1 (0.07–0.04 mg/100 g), B2 (0.05–0.03 mg/100 g), B3 (0.97–0.87 mg/100 g) and vitamin C (20.14–19.29 mg/100 g) decreased. Also the minerals (mg/100 g), calcium (16.15–15.77), potassium (409.71–409.62), magnesium (19.45–18.73), sodium (8.77–8.74), iron (0.42–0/35) and zinc (0.33–0.29) decreased. Micronutrient losses increased with increase in handling practices from the landing bay till it gets to the end users. Long-distance tomato transportation should be on smooth roads in the night inside rigid plastic crates to reduce bruises.

Keywords:

• Micronutrients
• fresh tomatoes
• stale tomatoes
• handling practices
• Umuahia metropolis

High Lights for Stale (NKUWA) Tomatoes

• Micronutrients of the fresh tomatoes decreases with distance, from the point of bulk purchase (landing bay) till it gets to the end user.

• Purchasing from the landing bay and consumption within 2 days of purchase offers maximum micronutrient.

• This study exposed the appropriate harmonization of the proper handling practices for the farmers and traders for maximum reduction of micronutrient loss.

• Stale or nkuwa tomatoes results in hidden hunger which is treat to health.

• This will guide the Government in formulating food chain policies or law for transporting and handling perishable agricultural produce like tomatoes in Nigeria.

• Packaging materials, good roads, good vehicles and transportation in the night will reduce the losses.

1. Introduction

Tomato (Lycopersicon esculentum) is a perishable savoury red edible fruit widely cultivated and consumed worldwide (Agrios, 2005) either raw or processed (Bhowmik et al., 2012), but mostly grind into paste and used in cooking stew and soups. It is also dried and milled into flour and used in preparing salads, sauces and drinks (Effiuwevwere, 2000; Zeb & Mehmood, 2004). Besides, it can be processed into drinks, puree, ketchup, and can be traditionally dried either as fruit pieces (Kumari & Singh, 2018). Different varieties abound with same nutritional characteristics (Zeb & Mehmood, 2004) but different colourations that varied from green, yellow, orange to red depending on their stage of maturity. Yellow varieties have high pro-vitamin A content than red ones while red tomato fruits contain lycopene, an anti-oxidant that contributes to protection against carcinogenic substances (Ajayi & Olasehinde, 2009). According to Zeb and Mehmood (2004), red colour is developed from carotenoids synthesized during maturation and it indicates maturity. During tomato ripening, edible acids, sugars and lycopene are synthesized; the fruit pulp is softened and its chlorophyll degraded.

Tomatoes have an appetizing colour, tasty, juicy and easily digestible endocarp (Barth et al., 2009; Effiuwevwere, 2000). It is among the widely consumed fresh fruit globally because of its contributions to a healthy well-balanced diet, vitamins (A, B, C and E), carbohydrates (fructose and glucose) minerals (phosphorous, sodium, potassium, calcium, magnesium and trace elements like iron, copper, zinc and dietary fibres) (Behravesh et al., 2006; Eni et al., 2010). Tomato is fairly rich in other micronutrients such as ascorbic acid among others (Bhowmik et al., 2012; Wogu & Ofuase, 2014). These micronutrients are not produced by the body but are needed for human life physiological functions that confer good health (Devi et al., 2014). They are also used as nutrient supplement, detoxificant and human system cleanser (Abhinaba, 2009).

Tomato paste extract contains antioxidants like lycopene, beta carotene and vitamin E that fight free radicals and slow atherosclerosis in the body (Bhowmik et al., 2012). Lycopene is a powerful antioxidant that prevents prostate cancer, skin’s harmful ultra violet rays, decreases the risk of breast, lung, stomach, bladder, uterine, head and neck cancers, protects neurodegenerative diseases, lowers urinary tract infections and reduces the cardiovascular risk associated with type 2 diabetes (Shidfar et al., 2010; Zdenka et al., 2010).

Tomato is one of the perishable climacteric fruits with a very short life span. Depending on the humidity and temperature, it may ripen very fast after harvesting with time to give soft and poor quality fruit liable to rejection (Onuorah & Orji, 2015). Spoilt or stale tomatoes, due to their cheapness, are oftentimes preferred by low-income consumers and mostly by food vendors whose aim is to maximize profits. As perishable fruits, they easily sustain bruises during loading, transportation; unloading, distribution and retailing, thereby result in postharvest deteriorations like loss of nutrients, colour and firmness. The losses are due to bad roads, types of trucks, packing baskets (long instead of flat) and the way they are stacked inside the trucks which constitute over-head weights on tomatoes at the bottom, thereby initiating cracks on easily bruised soft tomato tissue. Also, the inside of the baskets are rough and may piece the tomatoes. As the tomatoes are being loaded, transported, unloaded, distributed, stored and retailed, their soft biological structures are disrupted, thereby paving way for opportunistic pathogens. Microbial entry results in deteriorations due to more resident time and favourable weather conditions for them and enzyme degradation of the tissues. Nutrients are also lost (Barth et al., 2009; Oranusi et al., 2013).

In Umuahia, the trucks from the north where the tomatoes are farmed land at Ubani market from where they are distributed to the retail markets in baskets. Aside from the inevitable nutrient loss during this long-distance transportation, the activities of the retailers which vary with individuals also contribute. They sort the tomatoes into fresh and stale (popularly called nkuwa tomatoes) in unhygienic environments, wash with dirty water, display on dirty tables and in the sun. This work therefore explored the micronutrient loss of both fresh and nkuwa tomatoes sold in Umuahia metropolis due to handling practices orchestrated by transport distances and retailing activities.

2. Materials and methods

Both fresh and staled tomato samples (Figure 1–6) were procured from Ubani (11 Km from Umuahia), Isigate (center of Umuahia) and Orie-ugba (3.1 Km from Umuahia) retail markets. True representation of each sample was obtained by random purchase from six different tomatoes vendors in each retail market totalling 6 samples. The sampling was carried out at 14 d intervals between the markets. Each sample (about 500 g) was separately packaged in sterile Ziploc bag and immediately sent to the laboratory for analyses.

3. Sample preparation

Immediately in the laboratory, all the tomato samples were separately milled with variable speed kitchen electric blender (Philips, Model HR2001/70/AC 220-240 V) into their respective paste consistencies and packaged in an air-tight transparent glass bottle and stored in the refrigerator for analysis.

4. Analyses of the samples

4.1. Total carotenoid

The spectrophotometric method described by Onwuka (2018) was employed in the determination. Five grams (5 g) of the tomato paste sample was dissolved in 30 mL of absolute alcohol (ethanol) and 3 mL of 5% potassium hydroxide was added to it. The mixture was boiled under reflux for 30 min, cooled rapidly with running water and filtered. Thirty milliliters (30 mL) of distilled water was added and the mixture was transferred into a separating funnel. Three (3) portions of 50 mL of the ether were used to wash the mixture, the lower layer was discarded and the upper layer was washed with 50 mL of distilled water. The extract was evaporated to dryness and dissolved in 10 mL of isopropyl alcohol and its absorbance was measured at 325 nm. β-carotene content of the tomatoes was then calculated as shown:

Total carotenoid (mg/100 g) = $\frac{100}{w}\times \frac{au}{as}\times \mathrm{c}$

Where: au = absorbance of test sample

as = absorbance of standard solution

c = concentration of the test sample

w = weight of sample

4.2. Vitamin B₁ (thiamin)

The method according (Onwuka, 2018) was used. Five (5) grams of tomato samples was homogenized with 50 mL of ethanol sodium hydroxide. It was filtered into 100 mL flask; 10 mL of the filtrate was pipetted, and colour was developed by the addition of 10 mL potassium dichromate before reading at 430 nm wavelength in a spectrophotometer. A standard thiamin solution was prepared, diluted and absorbance evaluated at same wavelength. The readings were made with the reagent blank at zero. Thiamin was calculated using

$\mathrm{T}\mathrm{h}\mathrm{i}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\left(\mathrm{m}\mathrm{g}/100\mathrm{g}\right)=\frac{100}{\mathrm{W}}\mathrm{x}\frac{\mathrm{A}\mathrm{u}}{\mathrm{A}\mathrm{s}}\mathrm{x}\mathrm{C}\mathrm{x}\frac{\mathrm{V}\mathrm{f}}{\mathrm{V}\mathrm{a}}\mathrm{x}\mathrm{D}$

Where: W = Weight of sample analyzed

Au = Absorbance of test sample

As = Absorbance of standard solution

V_f = Total volume of filtrate

Va = Volume of filtrate analyzed

D = Dilution factor where applicable.

C = Concentration of the standard.

4.3. Vitamin B₂ (Riboflavin)

The method of Onwuka (2018) was used to determine the riboflavin content of the tomato paste samples. Five (5) grams of each sample was extracted with 100 mL of 50 % ethanol solution, shaken for 1 h and filtered. Ten (10) milliliters aliquot was treated with equal volume of 5 % potassium permanganate (KMnO₄) solution and 10 mL of 30 % hydrogen peroxide (H₂O₂). The mixture was allowed to stand on a water bath for 30 min, after which 2 ml of sodium sulfate (Na₂SO₄) solution was added. It was diluted to 50 mL with distilled water prior to measuring in spectrophotometer at 510 nm wavelength. The reading was taken with the reagent blank at zero. Riboflavin was calculated thus:

$\mathrm{R}\mathrm{i}\mathrm{b}\mathrm{o}\mathrm{f}\mathrm{l}\mathrm{a}\mathrm{v}\mathrm{i}\mathrm{n}\left(\mathrm{m}\mathrm{g}/100\mathrm{g}\right)=\frac{100}{\mathrm{W}}\mathrm{x}\frac{\mathrm{A}\mathrm{u}}{\mathrm{A}\mathrm{s}}\mathrm{x}\mathrm{C}\mathrm{x}\frac{\mathrm{V}\mathrm{f}}{\mathrm{V}\mathrm{a}}\mathrm{x}\mathrm{D}$

Where: W = weight of sample analyzed

A_u = Absorbance of the test sample

As = Absorbance of standard solution

V_f = Total volume of filtrate

V_a = volume of filtrate analyzed

C = Concentration of the standard

D = Dilution factor where applicable.

4.4. Vitamin B₃ (niacin)

The procedure described by Onwuka (2018) was used. Five (5) grams of each tomato paste samples were added to 50 mL of ammonium sulfate (NH₂SO₄) and shaken for 30 min. Three drops of ammonia solution was added to the sample and filtered into a 50 mL volumetric flask prior to addition of 5 mL of potassium ferrocyanide. This was acidified with 5 mL of 0.02N sulphuric acid and absorbance was measured in the spectrometer at 470 nm wavelength. A standard niacin solution was prepared and diluted. Ten (10) mL of the solution was analyzed. The reading was made with reagent blank at zero. Niacin content was calculated as

$\mathrm{N}\mathrm{i}\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{n}\left(\mathrm{m}\mathrm{g}/100\mathrm{g}\right)=\frac{100}{\mathrm{W}}\mathrm{x}\frac{\mathrm{A}\mathrm{u}}{\mathrm{A}\mathrm{s}}\mathrm{x}\mathrm{C}\mathrm{x}\frac{\mathrm{V}\mathrm{f}}{\mathrm{V}\mathrm{a}}\mathrm{x}\mathrm{D}$

Where W = weight of sample analyzed

A_u = Absorbance of the test sample

As = Absorbance of the standard solution

V_f = Total volume of filtrate

V_a = Volume of filtrate analyzed

C = Concentration of the standard

D = Dilution factor where applicable.

4.5. Vitamin C (ascorbic acid)

The method of Okwu and Josiah (2006) was used. Ten (10) grams of the tomato sample was extracted with 50 mL ethylenediaminetetraacetic acid (EDTA) solution for 1 h and filtered through a Whatman filter paper into a 50 mL volumetric flask. This was made up to the mark with the extracting solution. Twenty (20) mL of the extract was pipetted into a 250 mL conical flask, 10 mL of 30 % potassium iodide (KI) and also 50 mL of distilled water were added. This was followed by 2 mL of 1 % starch indicator and titrated against 0.01 M copper sulfate (CuSO₄) solution to a dark end point. Vitamin C was calculated thus

$\mathrm{V}\mathrm{i}\mathrm{t}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{C}\left(\mathrm{m}\mathrm{g}/100\mathrm{g}\right)=0.88\mathrm{x}\frac{100}{5}\mathrm{x}\frac{\mathrm{V}\mathrm{f}}{20}\mathrm{x}\frac{\mathrm{T}}{1}$

Where: V_f = Volume of the extract

T = Sample titre—blank titre

4.6. Calcium and magnesium

Calcium and magnesium content of the tomato paste samples were determined with the complexometric titration method of Onwuka (2018). Twenty milliliters (20 mL) of the tomato extract were measured into a conical flask and treated with pinches of the masking agents (hydroxylamine hydrochloride, sodium cyanide and sodium potassium ferrocyanide). The flask was shaken to dissolve the mixture before adding 20 mL of ammonia buffer to raise the pH to 10.00. The mixture was titrated against 0.02 N ethylenediaminetetraacetic acid (EDTA) solution using Eriochrome Black T as indicator to a permanent blue end point from deep red. A reagent blank was also titrated same. The titration value represents both Ca²⁺ and Mg²⁺ in the test sample. The analysis was repeated to determine Ca²⁺ alone by titrating with 10 % NaOH instead of ammonia buffer and solochrome dark blue indicator in place of Eriochrome black T. Total calcium and magnesium contents were calculated separately using: $\frac{\mathrm{C}\mathrm{a}}{\mathrm{M}\mathrm{g}}\left(\frac{\mathrm{m}\mathrm{g}}{\mathrm{m}\mathrm{g}}\right)=\frac{100}{\mathrm{W}}\hspace{0.17em}\times \hspace{0.17em}\frac{\mathrm{T}-\mathrm{B}\left(\mathrm{N}\mathrm{x}\mathrm{C}\mathrm{a}/\mathrm{M}\mathrm{g}\right)}{\mathrm{V}\mathrm{a}}\hspace{0.17em}\times \hspace{0.17em}\frac{\mathrm{V}\mathrm{f}}{1}$

Where W=Weight of sample

T = Titre value of sample

B = Titre value of blank

Ca = Calcium equivalence

Mg =Magnesium equivalence

Va = Volume of extract titrated

Vf = Total volume of extract

N = Normality of titrant (0.02N EDTA).

4.7. Potassium

The protocol of Onwuka (2018) was used. Standard solution of potassium was used to calibrate the instrument. The meter reading was at 100% E (emission) to aspire the top concentration of the standards. The % E of all the intermediate standard curves were plotted on linear graph paper with these readings. The sample solution was aspired on the instrument, and the readings (%E) were recorded. The concentration of the element in the sample solution was read from the standard curve and potassium calculated as follows:

$\mathrm{\%}\mathrm{P}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{u}\mathrm{m}=\frac{\mathrm{p}\mathrm{p}\mathrm{m}\times \hspace{0.17em}100\hspace{0.17em}\times \mathrm{D}\mathrm{F}}{1000}$

Where Df = Dilution factor

ppm = Part per million

4.7.1. Determination of potassium

Potassium was determined using the procedure described by Onwuka (2018). Potassium standard was prepared. The standard solution was used to calibrate the instrument read out. The meter reading was at 100% E (emission) to aspire the top concentration of the standards. The % E of all the intermediate standard curves were plotted on linear graph paper with these readings. The sample solution was aspired on the instrument, and the readings (% E) were recorded. The concentration of the element in the sample solution was read from the standard curve and potassium calculated as follows:

$\mathrm{\%}\mathrm{P}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{u}\mathrm{m}=\frac{\mathrm{p}\mathrm{p}\mathrm{m}\times \hspace{0.17em}100\hspace{0.17em}\times \mathrm{D}\mathrm{F}}{1000}$

Where Df = Dilution factor

ppm = Part per million

4.8. Zinc

Zinc was determined as described by Onwuka (2018). One gram of the tomato paste samples was first digested with 20 mL of acid mixture (650 mL concentrated HNO₃, 80 mL perchloric acid (PCA)). Five milliliters of the digest was collected and diluted to 100 mL with H₂O to serve as sample solution for atomic absorption spectroscopy (AAS) reading. Also, a standard solution of respective elements concentration of 0.0 to 1.0 was taken. The readings were used to plot a standard zinc curve for extrapolation, and zinc was calculated as follows:

$\mathrm{Z}\mathrm{n}=\frac{\mathrm{V}\mathrm{f}}{\mathrm{V}\mathrm{s}}\times \frac{1}{10}\times \frac{100}{\mathrm{W}}\times \mathrm{D}$

W= Weight of sample analyzed

Vf = Volume of extract

Vs = Volume of extract used

$\mathrm{D}$f = Dilution factor

4.9. Sodium

Sodium was determined using the flame photometry method (AOAC, 2010). Jaway digital flame photometry used was setup according to the manufacturer's instruction. It was switched on and allowed for 10 min to equilibrate. Standard sodium solutions was prepared separately and diluted in series to contain 10, 8, 6, 4 and 2 g of sodium. After equilibrating the instrument, 1 mL of each standard was aspirated into it and sprayed over the non-luminous flame. The optional density of the emission from each standard solution was recorded. Before filtering, sodium was put in place with standard and measured, the test sample extracts was measured in time and their graphs was plotted into standard curve which was used to extrapolate the content of sodium. Sodium content of the tomato sample was calculated as shown below:

$\mathrm{S}\mathrm{o}\mathrm{d}\mathrm{i}\mathrm{u}\mathrm{m}\left(\mathrm{m}\mathrm{g}/100\mathrm{g}\right)=\times /1000\times \mathrm{V}\mathrm{t}/\mathrm{V}\mathrm{a}\times \mathrm{D}\times 100/\mathrm{w}$

Where: X = concentration of the test element from the curve.

4.10. Iron

The iron content of the tomato paste sample was determined using the spectrophotometric method of AOAC (2010). Five grams (5 g) of the tomato paste were first digested with 20 mL of acids mixture (650 mL concentrated HNO₃, 80 mL perchloric acid and 20 mL concentrated H₂SO₄). The digest was diluted by making up to 100 mL with water. Two grams of the sample solution were pipetted inside a flask before 3 mL buffer solution, 2 mL hydroquinone solution and 2 mL bipyridyl solution were added. The absorbance reading was taken at wavelength of 520 nm and the blank was used to zero the instrument. Also, a standard solution of iron was prepared by dissolving 3.512 g of Fe (NH₄)_2. (SO₄). 6 H₂O in 10 mL of distilled water and two drop of 0.5 N HCl were added and diluted to 500 mL with distilled water. The iron standard was further prepared at different concentrations (2–10 ppm) by diluting with distilled water. Three milliliters (3 mL) of buffer solution, 2 mL of hydroquinone solution and 2 mL of bipyridyl solution were added. Absorbance reading was taken at 520 nm. The reading was used to plot a standard iron curve for extrapolation.

4.11. Statistical analysis

Data obtained were statistically analysed for one-way analysis of variance using the Statistical Package of Social Sciences version 23.0. The design was completely randomized, and the means were separated using Duncan multiple range test at 95% confidence level (p < 0.05).

5. Results and discussion

5.1. Vitamin content

5.1.1. Total carotenoid

The vitamin content results in Table 1 showed that total carotenoid content of fresh (640.44 µg/100 g) and nkuwa (598.36 µg/100 g) tomatoes from Ubani market were significantly (p < 0.05) higher than their respective counterparts from Isigate (623.24 and 586.64 µg/100 g) and Orie-ugba (627.06 and 579.64 µg/100 g) market locations. The least values from Orie-ugba (maximum loss) could be associated to the loss of wholesomeness arising from maximum transport bruises due to further distance (14.1 Km) from Ubani market. And microbial degradation of the tomato pulp (Okwunodulu et al., 2022). All these justified the influence of transportation and handling practices on total carotenoid loss. Ubani market (11.0 Km from Umuahia metropolis) is the major landing bay for all fresh tomatoes from the Northern part of Nigeria from where it is sold on whole sales in baskets to retailers. Isigate is a retail market at the centre of Umuahia Township while Orie-ugba is a near-by village market (3.1 Km from the Isigate market). These therefore point that the further away from Ubani market, the higher the transport and handling activities and nutrient losses. This agreed with the assertion that pro-vitamin A is well known to degrade faster in broken (bruised) fruits and vegetables (Onuorah & Orji, 2015). This could be visualized from the fresh look and slightly brighter colours of the fresh tomatoes (Plates 1, 3 and 5) than their nkuwa counterparts (Plates 2, 4, 6) in the entire market locations. Total carotenoid contains vitamin A precursor which aids in vision. Pro-vitamin A deficiency results in inability of the eye cells to quickly accommodate to dim light, thereby resulting in the condition known as night blindness (Onyeka, 2008). Consumption of nkuwa tomatoes over time may result in night blindness.

Plate 3: Isigate fresh tomatoes.

Plate 4: Isigate nkuwa tomatoes.

Plate 5: Orie-ogba fresh tomatoes.

Plate 6: Orie-ugba nkuwa tomatoes.

Table 1. Handling effects on the vitamin content of whole and stale tomato samples

Samples	Pro-vit A (µg/100 g)	Vitamin B1 (mg/100 g)	Vitamin B2 (mg/100 g)	Vitamin B3 (mg/100 g)	Vitamin C (mg/100 g)
WU	640.44^f ± 0.02	0.11^a ± 0.01	0.08^c ± 0.01	1.22^d ± 0.02	25.92^a ± 0.01
NU	598.36^c ± 0.04	0.07^ab ±0.01	0.05^ab± 0.01	0.97^b ± 0.01	20.14^c ± 0.01
WI	632.24^e ± 0.02	0.08^b ± 0.01	0.07^ab ±0.02	1.16^c ± 0.02	25.80^b ± 0.01
NI	586.64^b ± 0.02	0.05^c ± 0.01	0.04^a ± 0.01	0.91^a ± 0.01	19.35^d ± 0.01
WO	627.06^d ± 3.56	0.07^ab ±0.01	0.07^ab ±0.02	1.12^c ± 0.02	25.81^b ± 0.01
NO	579.64^a ± 0.02	0.04^d ± 0.01	0.03^a ± 0.00	0.89^a ±0.02	19.29^e ± 0.01

Plate 1: Ubani fresh tomatoes.

Plate 2: Ubani nkuwa tomatoes.

5.2. Vitamin B1

Same trend of pro-vitamin A loss was also observed in vitamin B1 for fresh and nkuwa tomato samples. There were no significant (p > 0.05) B1 variations between nkuwa tomatoes from Ubani and fresh tomatoes from Orie-ugba markets. This justified the influence of transport and retailed activities on vitamin B1 loss presumably due to extra losses as the tomatoes move from Ubani to Ori-ugba orchestrated by extra bruises and lag time for microbial spoilage. This also revealed little or no bruises on the tomatoes that landed at Ubani market may be because of their firmness, having been transported few hours after harvest which saw most of them still firm to withstand transport stress and can be equated with the fresh tomatoes at Orie-ugba market. Higher B1 loss of tomatoes from Orie-ugba than the rest of the markets may be affiliated to time lag from the time the tomatoes are sold to the time it gets to Orie-igba during which microbial and enzyme degradation must have acted on the bruised tomatoes and reduced the B1 content This also validated the fact that handling practice due to distance affects the nutrient content of tomatoes.

5.3. Vitamin B2

Vitamin B2 values of fresh and stale tomato samples from Ubani market were significantly (p > 0.05) higher than those from Isigate and Orie-ugba and could be traced to loss due to distance. There were no significant (p > 0.05) B2 difference between fresh and stale tomato samples from Isigate and Orie-ugba markets. This may be due to closer distance between them than that from Ubani which never had any significant (p > 0.05) handling loss. These results still maintained the correlation between distance and nutrient handling losses.

5.4. Vitamin B3

Significant (p < 0.05) higher B3 values from Ubani market than Isigate and Orie-ugba for fresh and nkuwa tomato samples were also observed as in vitamin B2. The B3 values of the fresh (1.22 mg/100 g) and nkuwa (0.97 mg/100 g) tomato samples from Ubani had the highest value while those from the fresh (1.12 mg/100 g) and nkuwa (0.89 mg/100 g) from Orie-ugba had the least. The results also maintained as in vitamin B2 that the loss is a function of distance and retail activities.

5.5. Vitamin C

Similar result trend as in pro-vitamin A was obtained in vitamin C content of both fresh and nkuwa tomato samples from all the three market locations. Fresh (25.92 mg/100 g) and nkuwa (20.14 mg/100 g) tomatoes from Ubani had the highest vitamin C content while those from Orie-ugba had the least, 25.81 and 19.29 mg/100 g, respectively, for fresh and nkuwa tomato samples. Also, similarity of vitamin C content of whole tomatoes from Isigate and Orie-ugba implied that the distance between them had no significant (p > 0.05) impact. Also, the time lag may have been so small that both microbial and enzyme degradation never imparted any significant (p < 0.05) effect on the Orie-ugba vitamin C content.

Values are means of triplicate determinations ± standard deviation. Mean values in the same column with different superscript are significantly different (p < 0.05). WU-whole tomatoes from Ubani, NU-nkuwa tomatoes from Ubani, WI-whole tomatoes from Isigate, NI-nkuwa tomatoes from Isigate, WO- whole tomatoes from Orie-ugba and NO- nkuwa tomatoes from Orie-ugba.

6. Mineral content

6.1. Calcium

The calcium results as presented in Table 2 indicated that the calcium content of whole (17.76 mg/100 g) and nkuwa (16.15 mg/100 g) tomato samples from Ubani market were significantly (p < 0.05) higher than their respective values from Isigate (17.61 and 15.83 mg/100 g) and Orie-ugba (17.65 and 15.77 mg/100 g) which are further away. There were no significant (p > 0.05) calcium variations between fresh and nkuwa tomatoes from Isigate and Orie-ugba. Shorter distance between them compared to that from Ubani market had no meaningful influence on their calcium content. The further the market is from Ubani market, the more the calcium content loss in both fresh and nkuwa tomato samples which portends handling losses due to distance. Bruises had been reported to significantly reduce the quality of tomato fruits through enzymatic degradation of the affected tissues like cell walls (Onuorah & Orji, 2015). Long-time consumption of nkuwa tomatoes might result in calcium deficiency which in turn may lead to osteoporosis and bone deterioration with increased risk of fractures (Piste et al., 2013).

Table 2. Handling effect on the mineral content of whole and stale tomato samples (mg/100 g)

Samples	Calcium	Magnesium	Potassium	Zinc	Sodium	Iron
WU	17.76^a ± 0.02	20.27^a ± 0.02	411.68^a ± 0.02	0.48^a ± 0.02	8.98^a ± 0.03	0.61^a ± 0.02
NU	16.15^c ± 0.04	19.45^c ± 0.02	409.71^d ± 0.01	0.33^b ± 0.01	8.77^d ± 0.02	0.42^d ± 0.01
WI	17.61^b ± 0.02	20.12^a ± 0.02	411.52^b ± 0.01	0.46^a ± 0.02	8.92^b ± 0.12	0.56^b ± 0.02
NI	15.83^d ± 0.02	18.75^d ± 0.01	409.64^e ± 0.02	0.30^b ± 0.01	8.74^e ± 0.03	0.37^e ± 0.02
WO	17.65^b ± 0.02	20.10^b ± 0.01	411.50^c ± 0.01	0.44^a ± 0.01	8.90^c ± 0.03	0.49^c ± 0.01
NO	15.77^d ± 0.02	18.73^d ± 0.01	409.62^e ± 0.02	0.29^b ± 0.01	8.75^e ± 0.02	0.35^e ± 0.02

Values are means of triplicate determinations ± standard deviation. Mean values in the same column with different superscript are significantly different (p < 0.05). WU-whole tomatoes from Ubani, NU-nkuwa tomatoes from Ubani, WI-whole tomatoes from Isigate, NI-nkuwa tomatoes from Isigate, WO- whole tomatoes from Orie-ugba and NO- nkuwa tomatoes from Orie-Ugha.

6.2. Magnesium

Significant (p < 0.05) higher magnesium content of fresh (20.27 mg/100 g) and nkuwa (19.45 mg/100 g) tomato samples from Ubani market than the other retail markets is an indication of significant (P < 0.05) impact of location on the magnesium content loss. Similarly, significant (p < 0.05) higher magnesium content of fresh (20.12 mg/100 g) and slight higher value of nkuwa (18.75 mg/100 g) tomato samples from Isigate than the respective values of 20.10 and 18.73 mg/100 g for fresh and nkuwa tomatoes respectively from Orie-ugba also substantiated the influence of location on magnesium content loss. It could be that the distance between the two markets never had any significant (p < 0.05) impact on the magnesium content.

6.3. Potassium

Potassium is the most abundant mineral in the tomato samples. Just like in calcium, potassium content of the fresh (411.68 mg/100 g) and nkuwa (409.71 mg/100 g) tomato samples from Ubani retail market was significantly (p < 0.05) higher than their counterparts from other markets. This could stem from handling losses due to distance, bad roads and because it is the landing place from where the tomatoes were distributed to other markets. Similarly, potassium values of whole tomato samples from Isigate were higher than that of Orie-ugba market which had the least. Their distance had significant (p < 0.05) impact on potassium only on fresh unlike in nkuwa tomatoes. May be the maximum potassium reduction must have taken place during transportation from Ubani to Isigate. Or the time lag from Isigate to Orie-ugba never enhanced enough enzyme reactions and microbial activities to effect reasonable change in the potassium content. This notwithstanding, the potassium content of nkuwa tomatoes from Isigate was slightly higher than that from Orie-ugba markets. Potassium is the most abundant intracellular fluid cation that significantly contributes in maintaining the normal cell functions as well as electrical activity of the heart. Any K⁺ imbalance will adversely affect the heart, cell function and health (Gerlin et al., 2007). Therefore, consumption of nkuwa tomatoes is not ideal due to potassium decrease which will in turn decrease the potassium: sodium ratio of the body. Adequate ratio helps to reduce high blood pressure.

6.4. Zinc

Unlike other minerals, the values of all the entire fresh tomato samples were higher (p < 0.05) than their nkuwa counterparts which corroborated the impart of distance and handling practices on the zinc content of both fresh and nkuwa tomato samples. Higher zinc values of fresh (0.48 mg/100 g) and nkuwa (0.33 mg/100 g) tomato samples from Ubani than those from Isigate (0.46 and 0.30 mg/100 g) and Orie-ugba (0.44 and 0.29 mg/100 g) justified the difference. Zinc is an essential micronutrient contained in more than 300 enzymes and hormones responsible for growth, healthy skin, teeth, bones, hair, nails, muscles, nerves and brain function. Zinc controls the enzymes that renew the cells in our bodies and helps in the formation of DNA. Zinc deficiency is an important public health problem, affecting large number of women and children (Devi et al., 2014). The deficiency may be more prevalent among the low income earners who relish more on nkuwa tomatoes.

6.5. Sodium

Sodium content of fresh and nkuwa tomato samples had same trend with that of zinc. Surprisingly, sodium content of the nkuwa tomato from Ubani (8.77 mg/100 g) is higher (p < 0.05) than (8.74 mg/100 g) and (8.75 mg/100 g) respectively from Isigate and Orie-ugba compared to slight (0.01 mg/100 g) higher value of Orieugba than Isigate. This negates the already established trend which could be equated to the retailer’s level of handling activities and type of tomato sampled. The general decreasing trend also concretised the impart of transport and retailer’s and buyer’s handling activities on the sodium loss. Sodium content of the entire tomato samples in this study is low. This could be of great importance to hypertensive patients as higher sodium content contributes to hypertension in susceptible individuals and increased calcium loss through urine (Gomez-Candela et al., 2011). Besides, higher (p < 0.05) potassium content of the fresh than nkuwa tomatoes substantiated the high blood pressure lowering potentials of the fresh than nkuwa tomatoes.

6.6. Iron

Iron content of whole tomato sample from Ubani market (0.61 mg/100 g) is significantly (p < 0.05) higher than those from Isigate (0.56 mg/100 g) and Orie-ugba (0.49 mg/100 g). There was no significant (p > 0.05) iron variation between nkuwa tomato samples from Isigate (0.37 mg/100 g) and Orie-ugba (0.35 mg/100 g). Despite this, the slight difference between them also validated the effect of location on iron loss. The slight variation is attributable to short distance between the two markets with little extra resident time for enzyme degradation. Iron is necessary for haemoglobin formation that carries oxygen in the blood, and myoglobin for transporting oxygen to the muscle tissues. Iron also helps in energy production and healthy immune system. Long-time consumption of nkuwa tomatoes may contribute to iron deficiency unless supplied by other foods in the diet of those that relish mostly on it.

6.7. Sodium to potassium ratio

There were no significant (p < 0.05) variations in the ratio for the entire fresh (0.022^a ±0.00) and nkuwa tomato (0.021^a ±0.00) samples in all the three market locations. But the values of the fresh samples were slightly higher which confirms higher sodium in fresh than in nkuwa tomato. Though is a slight disadvantage in terms of increasing blood pressure but higher potassium values will reduce that. Higher potassium content of the fresh over the stale tomatoes makes it a better preference by the hypertensive in this regard.

6.8. Correlation of vitamin C with calcium, magnesium, zinc and iron

Irrespective of state of the tomatoes (fresh or nkuwa), market locations and the extent of micronutrient variations, vitamin C correlated positively at 0.01 significant levels (p < 0.01) with calcium, magnesium, zinc and iron (Table 3). This confirmed that the induced damages on tomatoes due to transport and handling practices only reduced the micronutrient content but do not affect the absorption enhancement potentials of vitamin C on the minerals. Therefore, the fresh tomato samples may contain more available minerals compared to nkuwa which long time consumption may likely result in hidden hunger. This is in line with literature report that vitamin C enhances mineral absorption (MedicineNet MN, 2011). Nkuwa tomato consumption over time may not be worth it especially by the elderly and infants that need calcium for strong bones, iron for blood, zinc for immunity and magnesium for bone calcification.

Table 3. Correlation of vitamin C with calcium, magnesium, zinc and iron

		Calcium	Magnesium	Zinc	Iron	Vit C
Calcium	Pearson Correlation
	Sig. (2-tailed)
	N
Magnesium	Pearson Correlation	.969**
	Sig. (2-tailed)	.001
	N	6
Zinc	Pearson Correlation	.993**	.971**
	Sig. (2-tailed)	.000	.001
	N	6	6
Iron	Pearson Correlation	.937**	.943**	.972**
	Sig. (2-tailed)	.006	.005	.001
	N	6	6	6
Vit C	Pearson Correlation	.998**	.955**	.988**	.924**
	Sig. (2-tailed)	.000	.003	.000	.008
	N	6	6	6	6

Correlation is significant at the 0.01 level (2-tailed).

7. Conclusions

This study revealed higher micronutrient content in fresh than stale (nkuwa) tomatoes which decreased with increase in distance from Ubani market, the source of bulk purchase (landing bay), due to increase handling practices, enzyme and microbial deterioration of the tomato pulp. This exposed the health implication (hidden hunger) or consumption risk of nkuwa tomatoes often relished on by the poor income earners and some food vendors so as to protect life. Fresh tomatoes from Ubani market proved to be the best for consumption within Umuahia metropolis due to minimal handling activities followed by that from Isigate while that from Orie-ugba was the least. Excess handling of fresh and stale tomatoes should be avoided.

This study is a proper guide to farmers and retailers on how to reduce postharvest micronutrient loss in tomatoes through appropriate harmonization of proper handling practices. While the government will lean to formulate food chain policies or laws for transporting and handling perishable agricultural produce like fruits and vegetables in Nigeria. The Government will learn from this the need to repair the roads for safe transportation of agricultural produce.

This study is challenged by the variations in transport damages in each packaging basket due to tomato size variations, degree of ripeness, types of vehicles, basket stacking, time and distance covered. This and the variations in handling practices of the retailers made it difficult to have uniform loss. But with the six samples made from six different retailers per market and 14-day intervals between each market sampling, we could be able to make reliable representative sampling for the analysis.

Declaration of interest

There is no conflict of interest

Authors’ contribution

I.N. Okwunodulu: Conceived and drafted the original manuscript. S.C. Ozioko: Prepared the samples and analysis. F. U. Okwunodulu: Data collation and analysis. V.C. Ezeocha: Review and editing.

Submission declaration

All the authors approved the submission and declared that the said manuscript has not been previously published or under consideration elsewhere. I pledge on behalf of other co-authors that if the manuscript is accepted, we will not be published it anywhere in English or any other language or electronically in same form without the permission of the copyright holder.

Acknowledgement

In the absence of any external grant, the authors acknowledged Food Science and Technology Department of Michael Okpara University of Agriculture Umudike for the provision of space and reagents used.

Disclosure statement

No potential conflict of interest was reported by the author(s).