Regular Maize Research Articles

Bioplastic film making properties of quality protein maize (QPM) zein

AbstractBackground and ObjectiveQuality protein maize (QPM) has abundant γ‐zein, which crosslinks itself and other zeins through disulfide bonding. The work aims to develop zein bioplastics with better functionality by using QPM zein. Physical properties of cast QPM zein films from QPM maize were compared with zein films from regular maize types and commercial zein, all without added plasticizers.FindingsQPM zein contained 3.8% cysteine compared with 1.8%–2.7% in regular maize zeins and 1% in commercial zein and the QPM zein had a much higher proportion of γ‐zein. QPM zein films cast from glacial acetic acid (GAA) were opaque but absorbed the least liquid (≈16%) and swelled less (≈11%) after buffer immersion than the other zein films and aqueous ethanol‐cast films. Notably, the GAA‐cast QPM zein films became highly flexible after ambient storage, whereas the other zein films remained brittle.ConclusionsThe low buffer uptake and swelling of QPM zein films is attributed to crosslinking involving the cysteine‐rich γ‐zein polypeptides. Their flexibility is attributed to better solubilization of the zein in GAA and water molecules bound to the γ‐zein polypeptides acting as a plasticizer.Significance and NoveltyQPM zein can enable the formation of flexible zein bioplastics without added plasticizers.

Genome-Wide Association Study and Genomic Prediction on Plant Architecture Traits in Sweet Corn and Waxy Corn

Sweet corn and waxy corn has a better taste and higher accumulated nutritional value than regular maize, and is widely planted and popularly consumed throughout the world. Plant height (PH), ear height (EH), and tassel branch number (TBN) are key plant architecture traits, which play an important role in improving grain yield in maize. In this study, a genome-wide association study (GWAS) and genomic prediction analysis were conducted on plant architecture traits of PH, EH, and TBN in a fresh edible maize population consisting of 190 sweet corn inbred lines and 287 waxy corn inbred lines. Phenotypic data from two locations showed high heritability for all three traits, with significant differences observed between sweet corn and waxy corn for both PH and EH. The differences between the three subgroups of sweet corn were not obvious for all three traits. Population structure and PCA analysis results divided the whole population into three subgroups, i.e., sweet corn, waxy corn, and the subgroup mixed with sweet and waxy corn. Analysis of GWAS was conducted with 278,592 SNPs obtained from resequencing data; 184, 45, and 68 significantly associated SNPs were detected for PH, EH, and TBN, respectively. The phenotypic variance explained (PVE) values of these significant SNPs ranged from 3.50% to 7.0%. The results of this study lay the foundation for further understanding the genetic basis of plant architecture traits in sweet corn and waxy corn. Genomic selection (GS) is a new approach for improving quantitative traits in large plant breeding populations that uses whole-genome molecular markers. The marker number and marker quality are essential for the application of GS in maize breeding. GWAS can choose the most related markers with the traits, so it can be used to improve the predictive accuracy of GS.

Effects of dietary supplementation with herbal extract as methionine replacer on growth performance, meat composition, oxidative stability and liver gene expression in broiler chickens

Abstract In the present study, an herbal feed additive was tested for partial-to-complete replacement of synthetic methionine in poultry diets, along with its effects on performance, breast and thigh meat chemical composition, oxidative stability during refrigerated storage and the expression of five target genes in liver. In a 35 days trial, 600 one-day-old male chicks were randomly allocated to 4 groups with 10 replicates. Birds in the control group were fed a regular maize–soybean-based diet that covered DL-methionine needs while the second group (Meth40) was similar to control but contained only DL – Methionine at 40% of control diet. Diet in third group contained DLMethionine at 40% of control and the herbal feed additive Methiorep TMMeth40+Mrep) with extracts of Boerhavia diffusa, Azadirachta indica, Vigna mungo and Trigonella foenum-graecum. Diet of fourth group was formulated to totally replace DL Methionine by Methiorep TM (Mrep). Body weight gain and feed consumption were weekly recorded. At the end of the trial, all birds were slaughtered and 2 chickens per pen were selected for meat and liver sampling. The liver was tested for the expression of five target genes, namely Methionine synthase (MTR), Tyrosine aminotransferase (TAT), Spermidine synthase (SMS), Methionine sulfoxide reductase (MSRB1) and Betaine homocysteine S-methyltransferase (BHMT). The results showed that the Meth40 group had reduced body weight compared to the Meth40+Mrep group while the Control and Mrep groups had comparable weights. Feed intake and feed conversion ratio did not differ among the experimental groups. Carcass, breast and thigh meat yield were higher in the Mrep and the Control compared to Meth40 and Meth40+Mrep groups. Also, meat oxidation was significantly lower in herbal groups compared to the control group. After normalization to β-actin expression, quantitative real-time PCR analysis revealed an induction in the expression of MTR and SMS genes in the liver of both herbal treated groups. No changes were observed for the TAT, MSRB1and BHMT genes in the herbal treated groups compared to the control or the Meth40 group. In conclusion, herbal feed additives with specific plant extracts may be able to improve both growth performance and antioxidant activity of broiler chickens, phenolic content; yet, they may also support in amino acid efficient use of broiler.

Impact of Mineral Ions and Their Concentrations on Pasting and Gelation of Potato, Rice, and Maize Starches and Blends Thereof

AbstractBlends of starches can undergo additive or non‐additive pasting and gelation. As the impact of this remains undocumented, the effect of (partial) cation removal from waxy rice starch (WRS), regular rice starch (RRS), waxy maize starch (WMS), regular maize starch (RMS), and blends thereof with regular potato starch (RPS) on their pasting and gelation is studied. This is done by prior extraction with water or a solution of singly protonated EDTA. The (partial) removal of cations lowers the gelatinization temperatures of individual starches, causes pasting to start at lower temperatures and the level of viscosity breakdown to increase. This indicates lower granular stability when removing cations. Blends of RPS with untreated WMS/RMS and WRS/RRS show more additive pasting than blends of RPS with the same starches from which cations have been partly removed. Additionally, the presence of cations in cereal starches reduces swelling and viscosity development of RPS. The high peak viscosities, breakdown, and setback values suggest that more granular breakdown results in higher availability of molecules for increased network formation in blends of RPS with treated starches than in those with untreated starches. The obtained results are of interest for food applications where different starches are combined.

The dynamic transcriptome of waxy maize (Zea mays L. sinensis Kulesh) during seed development.

Waxy maize (Zea mays L. sinensis Kulesh) is a mutant of maize (Zea mays L.) with a mutation at Waxy1 (Wx1) gene locus. The seed of waxy maize has higher viscosity compared to regular maize. By now, we know little about the expression patterns of genes that involved in the seed development of waxy maize. By analyzing the transcriptome data during waxy maize seed development, we attempt to dig out the genes that may influence the seed development of waxy maize. The seeds of waxy maize inbred line SWL01 from six phases after pollination were used to do RNA-seq. Bioinformatics methods were used to analyze the expression patterns of the expressed genes, to identify the genes involved in waxy maize seed development. A total of 24,546 genes including 1611 transcription factors (TFs) were detected during waxy maize seed development. Coexpression analysis of expressed genes revealed the dynamic processes of waxy maize seed development. Particularly, 2457 genes including 177 TFs were specially expressed in waxy maize seed, some of which mainly involved in the process of seed dormancy and maturation. In addition, 2681, 5686, 4491, 4386, 3669 and 4624 genes were identified to be differential expressed genes (DEGs) at six phases compared to regular maize B73, and 113 DEGs among them may be key genes that lead the difference of seed development between waxy and regular maizes in milk stage. In summary, we elucidated the expression patterns of expressed genes during waxy maize seed development globally. A series of genes that associated with seed development were identified in our research, which may provide an important resource for functional study of waxy maize seed development to help molecular assisted breeding.

Comparison of the structure and properties of hydroxypropylated acid-hydrolysed maize starches with different amylose/amylopectin contents

Dually modified regular maize starch (RMS) and high-amylose maize starch (HAMS) were successfully prepared by first acid hydrolysis and subsequently hydroxypropylation. The effects of hydrolysis time (0–24 h) and propylene oxide (PO) content (10–30%) on the structure and physicochemical properties were investigated. The molar substitution (MS) of HAMS samples (up to 0.163) was generally higher than that of RMS samples (up to 0.149), suggesting the higher reactivity of amylose for hydroxypropylation. Besides, PO content had a greater influence on MS whereas the effect of acid hydrolysis time was minor. For both starches, the dual modifications did not cause apparent changes to the granule morphology but reduced gelatinisation temperatures and enthalpy; and a higher PO content led to higher relative crystallinity. These results suggest that hydroxypropylation occurred mainly on the surface of HAMS granules and had little influence on the compact granular structure, whereas this reaction impacted the internal structure of RMS much more. The rheological study shows the introduced hydroxypropyl bulky groups weakened the entanglements between amylose chains or amylopectin chains with long branches. Thus, this work provides insights into the rational design of modified starch products containing different amylose/amylopectin contents with tailored properties.

Cost Advantage of Biofortified Maize for the Poultry Feed Industry and Its Implications for Value Chain Actors in Nepal

Feed constitutes a significant cost of poultry production. We assess the cost-reducing effects of using Quality Protein Maize (QPM) in the poultry feed industry in Nepal. We also assess market structure of the poultry feed industry. Key informant interviews and short surveys were conducted with actors in the feed industry and maize value chain. We formulated a least-cost diet for broilers and layers with regular maize and QPM using a linear programing model. The results indicate that a ton of feed produced using QPM instead of regular maize reduces feed cost by at least US$7.10 for broilers and at least US$4.71 for layers of different ages. With the cost saving, the feed industry can pay a maximum of 4% price premium for QPM over regular maize. A strong linkage between feed industry and maize value chain actors is required for the feed industry to benefit sustainably from the use of QPM.

Understanding the fine structure of intermediate materials of maize starches

Here we concern the molecular fine structure of intermediate material (IM) fraction in regular maize starch (RMS) and Starpro 40 maize starch (S40). IM had a branching degree and a molar mass (Mw) somewhere between amylopectin (AP) and amylose (AM). Compared with AP, IM had more extra-long (Fr I) and long (Fr II) chains and fb3-chains (degree of polymerization (DP)>36), with a higher average chain length (CL). Also, IM contained less A-chains but more B-chains (both BS-chains with DP 3-25 and BL-chains with DP≥26), accompanied by longer B- and BL-chains, total internal chains (TICL) and average internal chains (ICL), and a similar average external chain length (ECL). Furthermore, relative to RMS-IM, the IM of S40 (with higher apparent amylose content than RMS) showed increases in relatively-long chains, e.g., Fr II, fb3-chains and BL-chains, but reductions in Mw, relatively-short chains (those with DP 6-12, etc.).

Natural variations in stearoyl-acp desaturase genes affect the conversion of stearic to oleic acid in maize kernel.

We identified 11 SAD genes, and mined their natural variations associated with the conservation of stearic to oleic acid, especially ZmSAD1 supported by both the QTL and an expression QTL. Maize oil is generally regarded as a healthy vegetable oil owing to its low abundance of saturated fatty acids. Stearoyl-ACP desaturase (SAD) is a key rate-limiting enzyme for the conservation of stearic (C18:0) to oleic (C18:1) acid. Here, 11 maize SAD genes were identified to have more divergent functions than Arabidopsis SAD genes. The genomic regional associations in a maize panel including 508 inbred lines identified 6 SAD genes significantly associated (P<0.01) with the C18:0/C18:1 ratio or the level of C18:0 or C18:1, one gene of which co-localized with a quantitative trait locus (QTL) and 5 of which co-localized with an expression QTL. ZmSAD1, supported by both the QTL and an expression QTL, had the largest effect on C18:0/C18:1. One nonsynonymous single-nucleotide polymorphism in exon 3 and one 5-bp insertion/deletion in the 3' untranslated region were further shown to contribute to the natural variation in C18:0/C18:1 according to ZmSAD1-based association mapping. Finally, selection tests of ZmSAD1 in teosinte, regular maize, and high-oil maize indicated that ZmSAD1 was not a selection target during the process of maize domestication and high-oil maize development. These results will guide the manipulation of the ratio between saturated and unsaturated fatty acids in maize.

THERMOANALYTICAL STUDY OF ACECLOFENAC FORMULATIONS WITH REGULAR MAIZE STARCH AND WAXY MAIZE STARCH

Production of tablets in pharmaceutical industry often is required to mixture the active ingredient (drug) with an inert material. Starch is shown as a good alternative material to be used as excipient. Thus, in this investigation the techniques: thermogravimetry and derivative thermogravimetry (TG/DTG), differential scanning calorimetry (DSC as well as thermomicroscopy were performed with aim to verify existence of interactions between aceclofenac (2-[2-[2-[(2,6-dichlorophenyl)amino]phenyl]acetyl]oxalacetic) with regular maize starch and waxy maize starch. Binary and physical mixtures of aceclofenac and starch in ratios 2:1, 1:1 and 1:2 (drug:starch) studied by the instrumental techniques showed that no interactions occurs between the drug and starches in any ratio, being maintained the properties of aceclofenac.

Insights into the hierarchical structure and digestion rate of alkali-modulated starches with different amylose contents

Combined analytical techniques were used to explore the effects of alkali treatment on the multi-scale structure and digestion behavior of starches with different amylose/amylopectin ratios. Alkali treatment disrupted the amorphous matrix, and partial lamellae and crystallites, which weakened starch molecular packing and eventually enhanced the susceptibility of starch to alkali. Stronger alkali treatment (0.5% w/w) made this effect more prominent and even transformed the dual-phase digestion of starch into a triple-phase pattern. Compared with high-amylose starch, regular maize starch, which possesses some unique structure characteristics typically as pores and crystallite weak points, showed evident changes of hierarchical structure and in digestion rate. Thus, alkali treatment has been demonstrated as a simple method to modulate starch hierarchical structure and thus to realize the rational development of starch-based food products with desired digestibility.

Zinc Absorption from Biofortified Maize Meets the Requirements of Young Rural Zambian Children ,

Background: The zinc content of maize, a major global food staple, is generally insufficient alone to meet the requirements of young children.Objectives: The primary objective of this study was to determine whether substitution of biofortified maize (34 μg zinc/g grain) for control maize (21 μg zinc/g) was adequate to meet zinc physiologic requirements in young children for whom maize was the major food staple. A secondary objective was to compare total daily zinc absorption when maize flour was fortified with zinc oxide to a total concentration of 60 μg zinc/g.Methods: Participants included 60 rural Zambian children with a mean age of 29 mo who were randomly assigned to receive 1 of 3 maize types (control, biofortified, or fortified) all of which were readily consumed (>100 g on 1 d). Total daily zinc intake (from maize and low-zinc relish) was determined from duplicate diet collections. Multiplication by fractional absorption of zinc, measured by a dual isotope ratio technique, determined the total daily zinc absorption on the day the test meals were given.Results: The mean ± SD total daily zinc intake (milligrams per day) from the biofortified maize (5.0 ± 2.2) was higher (P < 0.0001) than for the control maize (2.3 ± 0.9). Intake of zinc from the fortified maize (6.3 ± 2.6) did not differ from the biofortified maize. Fractional absorption of zinc from control maize (0.28 ± 0.10) did not differ from the biofortified maize (0.22 ± 0.06). Total daily absorption of zinc (milligrams per day) from the biofortified maize (1.1 ± 0.5) was higher (P = 0.0001) than for the control maize (0.6 ± 0.2), but did not differ from the fortified maize (1.2 ± 0.4).Conclusions: These results indicate that feeding biofortified maize can meet zinc requirements and provide an effective dietary alternative to regular maize for this vulnerable population. This trial was registered at clinicaltrials.gov as NCT02208635.

Pasting properties of blends of potato, rice and maize starches

In many food applications, chemically modified starches outperform their native starch counterparts. Starch blends are interesting clean label alternatives with potential for the food industry. Here, potato starch was blended with regular rice, waxy rice, regular maize or waxy maize starch in different ratios (100:0, 75:25, 50:50, 25:75 and 0:100). To elucidate the factors determining pasting, different total starch concentrations were used and swelling power and carbohydrate leaching were determined. During pasting, the starches in the blends impacted each other. Peak viscosities of the blends were lower than expected, especially at lower total starch concentrations (<6.0%) due to reduced swelling in the blend. At higher starch concentrations (>6.0%), the relation between peak viscosity and the percentage of a given starch in a blend was rather linear. Under such conditions, viscosity development is determined by granule rigidity rather than by swelling power. Minimum and end viscosities of the blends were intermediate between those of the individual starches at lower total starch concentrations. In contrast, at higher concentrations, minimum and end viscosities were as high as or even higher than the readings for potato starch, especially for blends of potato starch with rice or maize starch. Probably, reduced swelling led to a more conserved granular integrity during cooling which, along with interactions between leached molecules, can contribute to viscosity development. These results indicate that pasting of starch blends does not only depend on the individual starches and the blend composition, but also on the total starch concentration.

Qualidade fisiológica de sementes de milho doce classificadas pela espessura e largura

As sementes de milho doce apresentam qualidade fisiológica inferior à das sementes de milho comum, devido à influência de várias características, como o tamanho e a forma das sementes. Diante disto, este estudo objetivou avaliar a qualidade fisiológica de sementes de duas cultivares de milho doce (BR-401 e BR-402), classificadas, separadamente, quanto à espessura, por meio de peneiras de crivos oblongos (8/64" x 3/4, 9/64" x 3/4, 10/64" x 3/4, 11/64" x 3/4, 12/64" x 3/4 e 13/64" x 3/4), e quanto à largura, em peneiras de crivos redondos (17/64", 18/64", 19/64", 20/64", 21/64" e 22/64"). Para cada cultivar, os lotes classificados foram comparados com o lote sem classificação, seguindo delineamento inteiramente casualizado, em esquema fatorial 2x7, com quatro repetições. Os parâmetros biométricos avaliados foram: retenção em peneira, massa de 100 sementes e teor de água. A qualidade fisiológica foi determinada por meio da primeira contagem, germinação, teste de frio, envelhecimento acelerado, condutividade elétrica e emergência de plântulas no campo. A classificação em peneiras melhorou a qualidade fisiológica das sementes de milho doce. As sementes com espessura intermediária, para ambas as cultivares, em geral, apresentaram maior vigor. Quanto à largura, sementes maiores, para a cultivar BR-401, e de largura intermediária, para a cultivar BR-402, apresentaram melhor qualidade fisiológica.

Efficacy of quality protein maize in meeting energy and essential amino acid requirements in broiler chicken production

Quality protein maize (QPM), with almost double lysine and tryptophan in protein, is no different from regular maize (RM) in terms of quantity of energy and protein. The objective of the study was to assess whether QPM can substitute RM as an efficient energy source as well as requirement of essential amino acids in poultry feed. Experiments were conducted to determine apparent metabolizable energy (AME), digestible amino acid values, and utilization pattern of QPM and RM in chickens. AME of QPM was similar to RM. Lysine and threonine digestibilities were significantly (P≤0.05) higher in QPM than RM. Dietary replacement of RM by QPM at 50% or higher level significantly improved the body-weight gain. The overall feed conversion ratio (0–40 days) improved significantly in QPM compared to RM at 50% replacement level or higher. Abdominal fat content decreased by 40% and breast meat yield increased by 4.91% by dietary replacement of RM with QPM at 100% level. The protein concentration in serum increased linearly by increasing the level of replacement of RM by QPM. Serum cholesterol decreased significantly in the dietary group where RM was replaced by QPM at 100% level. Neither dressed weight nor giblet weight was influenced by replacement of RM by QPM or supplementing lysine to RM-based diet. However, the breast weight increased and abdominal fat content decreased significantly where RM was replaced by QPM at 50% level or higher. Our findings clearly indicated that feeding value of QPM was higher than RM in broiler chickens.

Quality Protein Maize for the Feed Industry in Kenya

Quality protein maize (QPM) has increased levels of lysine and tryptophan, limiting amino acids for monogastric animals, so its use in animal feed reduces the need for more expensive high-protein sources. The authors, through the application of a linear programming optimization model with the composition and prices of feed components used at the coast, show that the cost reduction from substituting QPM for regular maize in poultry feed for Kenya is 5% (mainly as a result of a reduction in fishmeal). The optimal ratios based on QPM and regular maize were calculated and formulated, and trials showed that broilers raised with either mixture had the same food intake, mortality and growth. Moreover, when the chickens were fried in the style popular at the coast, there was no difference in the taste of the meat between the two batches. If QPM were to replace regular maize in broiler feed in Kenya, a 5% cost reduction would translate into a gain of US$300,000. If the cost reduction were passed on to the broiler producers as a reduction in feed price, producers would be expected to gain on average US$32 per year. If the cost reduction were not passed on to the broiler producers, it would result in an extra profit for the feed industry.

The effect of acid dextrinisation on enzyme-resistant starch content in extruded maize starch

The enzyme-resistant starch (ERS) content in processed high amylose and regular maize starches has been studied, with and without acid dextrinisation. The physicochemical and structural characteristics of the starches were analysed using a variety of techniques. The increase in ERS in high amylose maize starch with dextrinisation was related to the formation of a critical molecular weight fraction (MW ∼ 20,000) that could rearrange structurally. Further dextrinisation reduced the processed starch MW to below where it could still form ERS. Regular maize starch containing less than 30% amylose did not increase its resistance to amylase digestibility with acid dextrinisation, probably due to impairment of amylose rearrangement by the numerous branched amylopectin chains. The ERS, which is likely to form during the enzyme-digestion process, is a linear molecule with a maximum degree of polymerisation (DP) of 30, irrespective of the starch source, processing conditions applied or type and amount of acid used.

Identification of resistance to corn-borer of transgenic maize inbred lines and hybrids with GFM Cry1A gene

AbstractSix transgenic maize lines with the fully modified gene GFM Cry1A were obtained and polymerase chain reaction (PCR) analysis of their T5 generation plants indicated that foreign genes could be stably inherited. Three hybrids (Simi25Bt, Tongdan24Bt and Jidan209Bt) were created using the transgenic lines and combined with regular maize inbred lines. The results of resistance identification of the transgenic inbred lines and hybrids showed that the difference of resistance among transgenic lines was very significant; there also existed a difference among individuals of the same line and among the three hybrids. Compared with the control inbred line (CK), the average of four transgenic inbred lines in the number of tunnels per stalk, larval tunnel length per plant and length of surviving larvae were decreased by 70%, 80% and 70%, respectively. Enzyme-linked immunosorbent assay (ELISA) testing showed that the average of Bt Cry1A protein expression level for six transgenic inbred lines was 0.16% total protein and the highest expression level was 0.19%. At maturity, compared with the control variety (CK), the larval tunnel length per plant of the three hybrids (Simi25Bt, Tongdan24Bt and Jidan209Bt) was decreased by 39.97%, 36.20% and 53.83%, respectively, which was a decrease of 43.36% on average. The investigation of agronomic characters showed that there was no significant difference between the improved hybrids and the control in plant height, ear length, row number per ear, kernel number per row and 100-kernels weight. It is thought that the GFM Cry1A gene can be applied to improve resistance to corn-borer, and maize inbred lines with the Bt gene can be directly applied to conventional maize breeding.

Effects of common bean enrichment on nutritional quality of tortillas produced from nixtamalized regular and quality protein maize flours

AbstractIn Mexico the tortilla is most commonly eaten in the form of ‘taco’; this is normally accompanied with other food, in particular the common bean. Tortillas made of quality protein maize (QPM) fortified with common bean might be a strategy to improve their protein quality. In this study, amino acids and mineral changes that occur during nixtamalization and the chemical and nutritional characteristics of regular, commercial and QPM tortilla–bean combination were assessed. After nixtamalization, protein from QPM nixtamalized maize flour was reduced from 8.1% to 7.2% (w/w). Tryptophan was also reduced from 12.1 to 11.1 g kg−1 protein. QPM maize retained a higher amount (P &lt; 0.05) of calcium (3180 mg kg−1) compared to regular maize (1820 mg kg−1). When nixtamalized maize flour of regular maize and commercial tortilla were combined with beans, protein content increased. The tryptophan and lysine contents in these tortillas were increased (P &gt; 0.05) also, but were significantly lower (P &gt; 0.05) than in tortilla made with QPM maize fortified with bean (22.7 and 69.9 g kg−1 protein, respectively). Mineral contents increased in tortilla–bean combination. The QPM and tortilla fortified with bean gave an improvement in protein quality and could contribute significantly towards human nutrition, especially in countries like Mexico where maize and beans are important components of the diet. Copyright © 2007 Society of Chemical Industry

Phosphorus Transformation in Pig Slurry due to Diet and Intermittent Aeration Treatments

The experiment was conducted to study the transformation of phosphorus (P) in slurry from pigs fed two different diets, i.e . the regular maize–soya bean meal diet with or without a supplement of 9% sugar beet pulp (SBP). The slurry was collected and treated either without or with aeration and intermittent aeration (aeration on/off ratio=10 h:14 h) at an airflow rate of 0·6 l m −3 s −1 for 15 days. Slurry sources and treatments were composed of a 2 by 2 factorial design. The results indicated that aeration increased (probability P < 0 · 01 ) the slurry pH by 0·5–0·8 within 24 h, from 6·5 to 7·0 for the SBP slurry, and from 6·9 to 7·7 for the control slurry, but the pH reached 7·6 and 8·0 for the SBP and control slurry in 3–4 days. The average pH of the SBP slurry was lower ( P < 0 · 01 ) than that of the slurry from the control diet (6·67 versus 7·38). However, little change in pH was observed in the non-aerated slurry. Aeration decreased total inorganic P, insoluble inorganic P, and soluble P, but increased organic P by approximately 30 mg l −1 . The average organic P in the slurry for both diets with aeration was about 17·4% higher than that in the same slurry without aeration. Aeration decreased insoluble inorganic P by about 7·2% and soluble P by about 4·5%. The mass balance of P fractions showed transformation of insoluble inorganic P into organic forms during the aeration stage. The insoluble inorganic P took about 68% of the total P in the slurry, so it is essential to perform solid–liquid separation prior to aeration to enhance the efficiency of soluble P removal because insoluble inorganic P is mainly contained in the slurry solids.